An individual who holds both a foreign nationality and Japanese nationality (dual nationality) must choose one nationality before the age of 22.

Those who obtain dual nationality after the age of 20 must choose one of the nationalities within 2 years of obtaining the nationalities.

Ministry of Justice, Homepage (Website): http://www.moj.go.jp/

Note 1 The information given is that confirmed as of July 2002. Note that a new system or system revisions may have been introduced after this date.

This information is from the CLAIR website. The Council of Local Authorities for International Relations (CLAIR) was established in July 1988 in response to rising concerns about local level internationalization in Japan.