JapanCan person under guardianship make a will?
No, a person under guardianship in Japan cannot make a valid will because they lack the legal capacity to do so under the Civil Code.
What the Law Says
Japanese law strictly ties the ability to make a will to mental capacity. A person placed under adult guardianship is deemed to lack the capacity to understand and express their true intentions regarding property disposition.
Under the Japanese Civil Code, only persons with full legal capacity may execute a valid will. A person under guardianship — whether under 'seinen hogo' (adult guardianship) or 'seinen kango' (adult curatorship) — is legally determined to lack the capacity to manage their own affairs, including making testamentary dispositions.
Article 962 of the Civil Code explicitly states that a will must be made by a person who has the capacity to make a will. This capacity is assessed at the time the will is made, and a court-appointed guardian’s existence is strong evidence of incapacity.
The Civil Code further clarifies in Article 5 that a person under guardianship is incapable of performing juristic acts without the consent of their guardian — and making a will is a unilateral juristic act requiring full capacity.
Statutory TextA will must be made by a person who has the capacity to make a will.
— Civil Code, Art. 962 — Capacity to Make a Will
Statutory TextA person under guardianship is incapable of performing juristic acts without the consent of the guardian.
— Civil Code, Art. 5 — Incapacity of Persons Under Guardianship
What to Do
Confirm the person’s current legal status through the family court registry or certified copy of the guardianship order.
If the person wishes to express final wishes, consult a lawyer about alternatives such as advance directives (though these are not legally binding for inheritance in Japan).
Family members may petition the family court for estate administration after death, but no will made during guardianship will be recognized.
If capacity is regained (e.g., guardianship is revoked), the person may then make a valid will — subject to proper formalities.
Sources
Not legal advice. This article is general information based on publicly available sources, written for educational purposes. Laws change and individual situations vary. Consult a licensed attorney in your jurisdiction before acting on anything you read here. Last reviewed: 2026-06-08.