Västanfjärd is a former municipality in the Southwest Finland region of Finland. It was consolidated on 1 January 2009 with Dragsfjärd and Kimito to form the new municipality of Kimitoön.
Before the merger, Västanfjärd was one of several small municipalities in the Archipelago Sea area of southwestern Finland. Its administrative functions were transferred to the newly created Kimitoön municipality, which now covers the territory that includes the former Västanfjärd.