Until January 1, 2007 Hashøj municipality was a municipality (Danish, kommune) in West Zealand County near the west coast of the island of Zealand (Sjælland) in Denmark. The municipality covered an area of 131 km², and had a total population of 6,632 (2005). Its last mayor was Troels Christensen, a member of the Venstre (Liberal Party) political party. The main town and the site of its municipal council was the town of Dalmose. The municipality was named after the hill Hashøjen near the town of Slots Bjergby.
Hashøj municipality ceased to exist as the result of Kommunalreformen ("The Municipality Reform" of 2007). It was merged with existing Korsør, Skælskør, and Slagelse municipalities to form the new Slagelse municipality. This created a municipality with an area of 571 km² and a total population of 76,185 (2005). The new municipality belongs to Region Sjælland ("Zealand Region").