Slagelse municipality is a municipality (Danish, Municipalities of Denmark) in Region Sjælland on the west coast of the island of Zealand (Sjælland) in Denmark. The municipality covers an area of 571 km², and has a total population of 77,457 (2008). Its mayor is Stén Knuth, a member of the Venstre political party.
The main city and the site of its municipal council is the city of Slagelse.
On 1 January 2007 Slagelse municipality was, as the result of Kommunalreformen ("The Municipal Reform" of 2007), merged with Hashøj, Korsør, and Skælskør municipalities to form an enlarged Slagelse municipality.
The ten largest urban areas in the municipality are:
Coordinates: 55°24′7.2″N 11°21′13.18″E / 55.402000°N 11.3536611°E