Kustavi is a municipality of Finland.
The municipality has a population of 892 (30 September 2012) and covers an area of 769.88 square kilometers (297.25 sq mi) of which 603.45 km2 (232.99 sq mi) is water. The population density is 5.36 inhabitants per square kilometer (13.9 /sq mi).
There are over 2,000 isles within the municipal area.
There are two ferry connections to Brändö and Iniö.
The municipality is unilingually Finnish even though it is located adjacent to the Swedish speaking Åland-region