Thai surnames, nicknames and Khun: what the name law actually says

Many explanations of Thai names still describe the 1913 Surname Act as if it were the rulebook. It is not: section 3 of the Personal Name Act of 1962 repealed it, and the law you will actually meet on a Thai form is the 1962 Act as amended in 1987 and 2005.

This guide sets out what that law says about surnames, middle names and name changes, what it does not say about nicknames, and how to address people politely. The legal detail comes from the Office of the Council of State's consolidated text of the Act, published by the Department of Provincial Administration's registration bureau; the etiquette comes from a US government business guide.

The 1913 Act and what replaced it

The Personal Name Act (พระราชบัญญัติชื่อบุคคล พ.ศ. ๒๕๐๕) was signed on 15 November 1962 and published in the Royal Gazette on 23 November 1962, in volume 79, part 104, special issue, page 5. It came into force the day after publication.

Its section 3 repeals four earlier laws by name. The first is the Surname Act of B.E. 2456 (พระราชบัญญัติขนานนามสกุล พระพุทธศักราช ๒๔๕๖), the law usually dated to 1913 in the Western calendar. The others are a 1922 royal decree adding to it, a second Surname Act of B.E. 2481 and an earlier Personal Name Act of B.E. 2484.

That is the part of the 1913 story that can be confirmed from the current statute. The text of the 1913 Act itself, held in the Royal Gazette archive, could not be opened for this guide, so its original clauses are not described here.

The 1962 Act kept continuity with the old system in one important way. Section 10 says that surnames lawfully registered before the Act came into force are treated as registered under it, so family names created under the earlier laws remain valid.

The Act has been amended twice. A 1987 amendment gave widows the choice of keeping a husband's surname or returning to their own, and a 2005 amendment rewrote the rules on married names, middle names, sharing surnames and fees.

Both amendments were published in the Royal Gazette, the 1987 one on 28 December 1987 in volume 104, part 270, and the 2005 one on 19 January 2005 in volume 122, part 7 kor, and the consolidated text used here carries the Office of the Council of State's watermark and notes which sections each amendment changed.

The 2005 changes followed a court ruling. The amendment's stated reasons cite Constitutional Court ruling 21/2546, which found the 1962 Act's original section 12, the section that now deals with married surnames, unconstitutional, as well as loose rules that let people borrow other families' surnames as middle names.

The same note lists practical reasons too. The old procedure did not suit electronic public services, only the original registrant could let others share a surname, which caused problems once that person had died, and the fee rates had been in use for a long time.

Three legal parts of a name

The Act defines exactly three kinds of name. Section 4 describes the given name (ชื่อตัว) as a person's own name, the middle name (ชื่อรอง) as a name that follows the given name, and the surname (ชื่อสกุล) as the name of the family line.

Section 5 makes two of them compulsory. "ผู้มีสัญชาติไทยต้องมีชื่อตัวและชื่อสกุล และจะมีชื่อรองก็ได้": a person of Thai nationality must have a given name and a surname, and may have a middle name.

Nicknames are not on that list. Nothing in the Act defines, registers or regulates a nickname, which means the short name a colleague asks you to use has no legal standing under this law.

No official source read for this guide explains why Thai people use nicknames; the only government mention found is the US trade guide's statement that "Nicknames are common in Thailand."

The Act also restricts given and middle names. Section 6 says a given name must not coincide with or aim to resemble the names of the King or Queen or a rajathinnam, a formal title name, and must not be rude.

Section 7 deals with one historical category. A person who was granted a noble title (บรรดาศักดิ์), or who held one and left it without being stripped of it, may use the rajathinnam from that title as a given name or middle name.

Middle names carry an extra rule. They must not duplicate another person's surname, except where a spouse uses the other spouse's surname as a middle name with consent, or a child uses the mother's or father's original surname as a middle name.

Rules a new surname must meet

Section 8 sets five tests for a new surname. It must not coincide with or aim to resemble the names of the King or Queen; must not resemble a rajathinnam, unless it is the applicant's own or a direct ancestor's or descendant's; must not duplicate an existing surname; must not contain rude words; and must meet a length limit.

The duplication test is set out in full. A surname must be "ไม่ซ้ำกับชื่อสกุลที่ได้รับพระราชทานจากพระมหากษัตริย์ หรือชื่อสกุลที่ได้จดทะเบียนไว้แล้ว": not the same as a surname granted by the King or one already registered.

The length limit is precise. A surname must have "พยัญชนะไม่เกินสิบพยัญชนะ", no more than ten consonants, unless it uses a rajathinnam. The cap is written in consonants (พยัญชนะ), not in letters, so the Act itself does not limit how long a surname looks once it is written out or transliterated into English.

Royally granted surnames are recorded separately. The Fine Arts Department publishes a catalogue of surnames granted from the seventh reign onwards, and its description says the book includes an appendix comparing surnames with Chinese clan names (แซ่). The catalogue page dates the publication to January 2020, gives it 218 pages and lists indexes of title names and original names. The book itself sits behind a login and was not read.

Sharing is allowed, copying is not. Under section 11 the person who registered a surname may allow any Thai national to use it, and since 2005, if the registrant has died, the closest living descendant who uses the surname can give that permission. The permission is complete once the registrar issues the certificate.

Marriage, divorce and name changes

Married names follow section 12 as rewritten in 2005. Spouses may agree to use either spouse's surname, or each may keep their own, and they can make or change that agreement at the time of marriage or later.

The end of a marriage has its own rule. Under section 13, after divorce or annulment the spouse who used the other's surname returns to their original surname; after a death the survivor may keep the surname, but returns to their own on remarrying.

Women who were already using a husband's surname before the 2005 amendment may keep it, according to that amendment's transitional section, without losing the right to return to their own surname.

Changing a given or middle name is a local matter. Section 16 says you apply to the local registrar where you are on the house register, and the registrar issues a certificate if the new name does not break the Act.

The registrars themselves are defined in section 4. The term covers the local registrar, the provincial registrar and the Central Registrar, all appointed by the Minister responsible for the Act, who under section 20 is the Minister of Interior.

Registering a new surname takes longer. Section 9 sends the application from the local registrar up to the Central Registrar for approval, although since 2005 a local registrar linked to the central registration network, as notified by the Ministry of Interior, can approve it without that step. Once the surname is approved, the local registrar registers it and issues a certificate.

Changing an existing surname follows the same route. Section 17 says a person who already has a surname and wants a new one applies to the local registrar, and the application is then handled under the section 9 procedure.

A refusal can be appealed. Section 18 gives the applicant 30 days from learning of the decision to appeal to the Minister through the local registrar, and "คำวินิจฉัยของรัฐมนตรีให้เป็นที่สุด": the Minister's decision is final.

The Act also covers children without a known surname. Section 15 lets carers, or the owners of hospitals, welfare homes and childcare institutions, register a surname for Thai children in their care who have none.

The Act's fee schedule, as amended in 2005, is a ceiling rather than a price list. Section 20 lets the Minister of Interior set fees by ministerial regulation at no more than the rates attached to the Act, and the ministerial regulation itself was not read for this guide.

These fees apply to Thai nationals using the registration system, and a new surname is issued as a certificate by the registrar.

Addressing people politely

The everyday rule is simpler than the law. The US International Trade Administration's guide for business travellers, last published on 21 April 2026, says: "“Khun” is the Thai form of address for Mr., Mrs., and Ms. and is followed by a first name or nickname."

That is the practical answer to the surname question for most visitors. In conversation, on the guide's description, you address someone by Khun and their first name or nickname, not their surname.

Titles take priority for some people. The same guide says "government officials and doctors should be addressed by their title, such as Secretary, Minister, or Doctor, followed by the individual’s first name."

Order matters in a group. The guide notes that "Respect for hierarchy is essential, so it is important to address the most senior person first", and that communication tends to be indirect to avoid confrontation.

Tone matters as much as the name. The guide says losing one's composure means losing face and others' respect, and that raising your voice or showing frustration is considered inappropriate.

Greetings follow the same logic. The guide describes the wai as "placing your palms together in a prayer-like position at chest level and giving a slight bow", used both on meeting and leaving, and adds that Thais may also be familiar with a Western-style handshake.

Business cards are exchanged at every meeting, according to the guide, and "it is considered impolite to write on someone’s business card in their presence". If you need to note a nickname, do it somewhere else.

The guide adds a few rules about the body that come up when you meet people at home. It says the head is sacred and the cleanest part of the body, so Thais consider it rude to touch someone on the head, that pointing at anything with your feet is rude, that shoes should be removed before entering a home or temple, and that you should not cross your legs in the presence of the elderly or monks. Visits to temples bring a separate set of expectations, covered in the guide to temple dress and conduct.

Names on forms and documents

The legal name and the name you hear socially can differ completely. Because nicknames have no legal status under the Act, the name on a Thai person's official records is their given name, any middle name, and their surname, as registered under the 1962 law.

That matters when you book something for, or with, a Thai friend or colleague. Ask for the name exactly as it appears on their identity document rather than the name you use every day.

The same caution applies to middle names. The Act allows an optional middle name, and since 2005 that can be a spouse's surname or a parent's original surname, so a form that has no middle-name field may need the person's guidance on where to put it.

For your own paperwork, the relevant documents are your passport and entry forms rather than Thai name law. The guide to what to arrange before you fly covers the entry paperwork.

Name changes are also worth knowing about. The Act lets Thai nationals change a given name, a middle name or a surname through the local registrar, so a person's registered name on an old document may differ from the one on a new one; if a booking or form must match an identity document, use the name on the current document.

A useful decision rule: use the nickname in conversation, the registered name on anything official. If you are unsure which is which, ask, and write down the registered spelling for bookings.

Myths the statute corrects

The first myth is that the 1913 Surname Act still governs Thai names. It was repealed in 1962, and the rules you will meet today come from the Personal Name Act as amended.

The second is that a nickname is some kind of official second name. The Act knows only three name parts, given, middle and surname, and none of them is a nickname.

The third is that every Thai surname is unique. The Act bars a new registration from copying an existing surname, but it also lets a registrant share a surname with other Thai nationals, and surnames registered under the earlier laws were carried over.

Another is that a Thai woman must take her husband's surname on marriage. Since the 2005 amendment, section 12 lets spouses agree to use either spouse's surname or to keep their own, and the agreement can be changed later.

The last is that there is an official explanation for why surnames look long. There is a ten-consonant cap and a no-duplicates rule in the law, but no official source read for this guide gives a reason for surname length.

What this guide does not cover

The original text of the 1913 Surname Act could not be verified. Its Royal Gazette file was blocked to automated access and, when it loaded in a browser, was a scanned image that could not be read, so this guide describes the 1913 law only through the 1962 Act that repealed it. The dates also do not line up neatly: the 1962 Act calls the law the Surname Act of B.E. 2456, while the Gazette file for it sits in a folder for 2455, and this guide does not give a day or month for the 1913 law.

No official source was found that explains why Thai surnames are long or why nicknames are used, so neither question is answered here. The ministerial regulation that sets the actual current fees was not read; the figures given are the Act's ceilings.

The Fine Arts Department's catalogue of royally granted surnames was not read beyond its public description, and this guide does not comment on the monarchy or on royal naming practice beyond what the Act states. Official guidance on how Thai names should be entered on airline or hotel bookings was not found, and the Royal Institute's dictionary entry for Khun could not be opened.