Unzen (雲仙市 Unzen-shi) is a city located in Nagasaki Prefecture, Japan, on the northern tip of Shimabara Peninsula, facing Ariake Bay in the east and Mount Unzen to the south.
As of March 2008, the city has an estimated population of 48,123 and a population density of 233 persons per km². The total area is 206.92 km².
The modern city of Unzen was established on October 11, 2005, from the merger of the towns of Aino, Azuma, Chidiwa, Kunimi, Minamikushiyama, Mizuho and Obama (all from Minamitakaki District).
Obama Onsen is located in Unzen City. The poet Saito Mokichi wrote a verse about the beauty of this hot spring.