Seki (関市, Seki-shi) is a city located in Gifu Prefecture, Japan. The city was founded on October 15, 1950.
On February 7, 2005, the towns of Mugegawa and Mugi, and the villages of Horado, Itadori and Kaminoho (all from Mugi District) were merged into Seki.
As of July 2011, the city has an estimated population of 91,239 and a population density of 190 persons per km2. The total area is 472.84 km2.