A person who is born with parents who both hold Thai nationality automatically acquires Thai citizenship, whether they were born inside or outside of Thailand. A person born with one alien parent does not automatically acquire Thai citizenship. Citizenship depends on the immigration status and the marriage status of the parents. A person born to either a Thai father or mother, regardless of birth place, may apply for Thai citizenship.
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A foreigner who would like to obtain Thai Citizenship must go through the naturalization process. You can file the application with the competent official according to the form and in the manner prescribed in the Ministerial Regulations.  It is under The Interior Minister’s discretion to approve or deny an application.
An applicant who wishes to apply for naturalization as a Thai citizen must have the following qualifications:
1. of legal age according to the Thai law and the law under which he has nationality;
2. have a good behavior;
3. with a regular occupation;
4. have resided in the Thai Kingdom for a consecutive period of not less than five years on the day of filing the application; and
5. proficient in Thai language as prescribed in the Ministerial Regulations.
The qualifications 4 and 5 do not apply to the following applicants;
1. if he or she has rendered distinguished acts or deeds for the Kingdom of Thailand;
2. being the child, wife, or husband of a person who has undergone Thai naturalization process or has recovered Thai nationality;
3. had previous Thai Nationality;
4. if he is a husband of a Thai national.
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Foreign applicants residing in Thailand with children who are not of legal age may concurrently apply for such naturalization for his children.  In this case, such children shall be exempt from possessing the qualifications 1, 3, 4 and 5.
1. A guardian, under a court order, may apply for naturalization for an incompetent person.  The guardian needs to present an evidence to prove the person’s birth in Thailand. In this case, such person shall be exempted from possessing the qualifications 3 and 5. Making an affirmation of loyalty to Thailand shall be at the Minister’s discretion.
2. A ruler of public foster home, with the children’s permission and with the Minister’s conformity, may apply for naturalization for children of legal age. It is necessary that the children are staying under the responsibility of such foster home for not less than 10 years. In this case, such person shall be exempted from possessing the qualifications under 1 and 3.
3. A Thai person may apply for naturalization for the adopted child who is of legal age. The adopted child must be registered as a legitimate child of the Thai person for not less than 5 years. The Thai person must show evidences proving the birth of the child in Thailand. Â In this case, such persons shall be exempt from possessing the qualifications 1 and 3.
A Thai national, married to a foreigner and has acquired his/her spouse’s nationality, do not lose Thai nationality.  Losing the Thai nationality may happen if he/she renounces his/her Thai nationality by declaring his/her intention to the authority or by the Government of the Kingdom of Thailand’s revocation. A person who has renounced Thai nationality may apply for recovery of Thai nationality in case of marriage dissolution for whatever reason. They must file the application according to the form and in the manner prescribed in the Ministerial Regulations.
