Kustavi (Finnish pronunciation:[ˈkustɑʋi]; Swedish:Gustavs) is a municipality of Finland.
It is in the province of Western Finland and is part of the Southwest Finland region. The municipality has a population of 891 (30 June 2015) and covers an area of 769.88 square kilometres (297.25sqmi) of which 603.45km (232.99sqmi) is water. The population density is 5.35 inhabitants per square kilometre (13.9/sqmi).