Naka-ku is one of four wards of Okayama, Okayama Prefecture, Japan. The ward has an area of 51.24 km² and a population of 138,949. The population density is 2,711 per square kilometer. The name means "Central Ward." The wards of Okayama were established when Okayama became a city designated by government ordinance on April 1, 2009.