Reviewed by ThaiLawOnline, a licensed Thai law firm practising in Thailand since 2006. Thai lawyer of record: Wichuda Atthamethakon, LL.M., Thai Bar Licence 3149/2556.
Last updated on September 5, 2026
Incapacity (คนไร้ความสามารถ for an incompetent person, คนเสมือนไร้ความสามารถ for a quasi-incompetent person, also translated incompetence and quasi-incompetence) is the legal status of an adult whom a court has found unable, wholly or partly, to manage their own affairs. Sections 28 to 36 of the Civil and Commercial Code create two levels: full incompetence, which places the person under a guardian, and quasi-incompetence, which places them under a curator whose consent is needed for important transactions. The status exists only from the court’s order, not from the medical condition itself.
Table of Contents
The two levels the Code recognises
Incompetence (Section 28). A person of unsound mind may be adjudged incompetent by the court on the application of a spouse, ascendant, descendant, existing guardian or curator, the person caring for them, or the public prosecutor. The person is placed under guardianship and a guardian is appointed. Under Section 29 every juristic act done by an incompetent person is voidable. Section 30 covers the gap before any order: an act by a person of unsound mind not yet adjudged incompetent is voidable only if done while of unsound mind and the other party knew it.
Quasi-incompetence (Section 32). This applies to a person who, through physical or mental infirmity, habitual prodigality, habitual intoxication or a similar cause, cannot manage their affairs properly. The court places them under curatorship. The person keeps capacity for ordinary life, but Section 34 lists acts that need the curator’s consent: investing capital, borrowing or lending money, accepting or renouncing an inheritance or a gift, disposing of immovable property, going to law, and other acts the court specifies. An act done without that consent is voidable.
Where foreigners meet the rules in practice
The typical case is an elderly foreign resident with dementia or after a stroke, a Thai spouse or child who needs authority over bank accounts, a condominium or medical decisions, and a bank refusing to act on a signature it doubts. A power of attorney does not solve this, because under Section 826 an agency ends when the principal becomes incompetent. The petition goes to the Juvenile and Family Court with medical evidence, usually a psychiatric report from a government hospital, and the court hears the family and, where possible, sees the person.
Documents made while capable remain the better route. A will made before the order stands, but Section 1704 makes a will by a person already adjudged incompetent void. A living will under Section 12 of the National Health Act B.E. 2550 lets a competent person refuse life-prolonging treatment in advance; it must be signed while the declarant is still mentally competent.
Incompetent, quasi-incompetent and minor compared
A minor under 20 is also a person of limited capacity, but by age rather than by court order: acts need the consent of the holder of parental power, with exceptions for acts that only benefit the minor and for daily necessities. Incompetence and quasi-incompetence must be declared by a court and end only when the court revokes the order because the cause has ceased.
| Status | Section | Who acts for the person | Effect on transactions |
|---|---|---|---|
| Minor | Sections 19 to 21 | Holder of parental power or guardian | Acts without consent voidable, with exceptions |
| Quasi-incompetent | Sections 32 to 36 | Curator (phu phithak) | Listed acts need curator’s consent or are voidable |
| Incompetent | Sections 28 to 31 | Guardian (phu anuban) | All juristic acts voidable; guardian acts instead |
Frequently asked questions
Can a foreigner be declared incompetent by a Thai court?
Yes. Sections 28 and 32 apply to anyone within the jurisdiction of the Thai courts, and petitions are regularly filed for foreign residents with dementia or severe illness. The court needs medical evidence and normally appoints the Thai spouse or an adult child as guardian, which gives them authority over Thai bank accounts and property.
What is the difference between incompetent and quasi-incompetent in Thailand?
An incompetent person under Section 28 is of unsound mind and loses capacity entirely; a guardian acts for them and any act they do themselves is voidable. A quasi-incompetent person under Section 32 has a lesser infirmity and keeps capacity for ordinary acts, but needs a curator’s consent for the important transactions listed in Section 34.
Does a power of attorney still work if the person becomes incompetent?
No. Under Section 826 an agency ends when the principal becomes incompetent, and Thai banks and the Land Office will not act on a power of attorney once they know of the incapacity. The family must then obtain a court order appointing a guardian or curator to deal with the person’s affairs.
See also: guardian, void and voidable juristic acts, Juvenile and Family Court, terminal illness, and the full guides to the living will in Thailand and making a last will in Thailand.
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