Tokyo High Court dismissed Tuesday an appeal by a group of people claiming the country's ban on its citizens from holding foreign nationality violates the Constitution.
The decision by the high court endorsed a district court ruling in January 2021 that deemed dual citizenship "could cause conflict in the rights and obligations between countries, as well as between the individual and the state."
The eight plaintiffs, who were born in Japan but now live in Europe, plan to appeal the ruling to the Supreme Court.
An article of the Nationality Law states that Japanese citizens who acquire non-Japanese nationality on their own instigation automatically lose their Japanese nationality, effectively banning dual citizenship.
The plaintiffs have said foreign nationality is necessary to facilitate their work and lives abroad, but that they hope to also maintain their Japanese citizenship.
They argued that the clause stripping people of Japanese nationality violates the Constitution, which guarantees the right to pursue happiness and equality under the law.
Swiss resident Hitoshi Nogawa, 79, who led the plaintiffs, said Japanese nationality forms part of his identity.
"I would like to present (my feelings on the matter) before the Supreme Court," he told a news conference following the ruling.