Sakai-ku (堺区) is a ward of the city of Sakai in Osaka Prefecture, Japan. The ward has an area of 23.69 km² and a population of 147,413. The population density is 6,223 per square kilometer.The wards of Sakai were established when Sakai became a city designated by government ordinance on April 1, 2006. The city has its municipal headquarters in Sakai-ku and Sakai City Museum is located in the area.