Nishi-ku (西区?) is a ward of the city of Sakai in Osaka Prefecture, Japan. The ward has an area of 28.62 km² and a population of 133,583. The population density is 4,667 per square kilometer. The name means "West Ward."
The wards of Sakai were established when Sakai became a city designated by government ordinance on April 1, 2006.
Coordinates: 34°32′5.99″N 135°27′50.31″E / 34.5349972°N 135.4639750°E / 34.5349972; 135.4639750