The town of Iwaki in Akita Prefecture will let 18- and 19-year-olds vote in a plebiscite Sunday on merging with another city.
It will be Japan's first plebiscite granting teenagers the vote.
Voters will pick between Iwaki merging with the city of Akita or the city of Honjo.
Mayor Koichi Kato said he decided to lower the voting age from 20 to 18 to allow more people to participate in deciding the town's future.
"Young people's participation is indispensable for the creation of a new urban area," particularly at a time when the birthrate is shrinking and the population is aging," Kato said.
Anyone who has lived in the town continuously for three months or longer, is 18 or older and is either a Japanese citizen or a permanent foreign resident can cast a ballot.