the Government of Thailand

“ A person who wishes to change his existing family name shall make an application therefor to a local registrar in charge of the locality where his name is entered in a household register in pursuance of the law on civil registration. ”

“ In the event that the registrar denies an application for last name registration, the applicant shall be entitled to lodge with the Minister an appeal against the order of the registrar. The lodging must be made within thirty days from the date the appellant is informed of the order and the appeal shall be filed to the local registrar. ”

“ A woman widowed by divorce shall surrender the last name of her husband and use her former last name instead.
§ 14 [2]
A woman widowed by death of her husband may continue to use the last name of her husband or use her former last name instead. ”