Kustavi (Finnish pronunciation: [ˈkustɑʋi]; Swedish: Gustavs) is a municipality of Finland.

The larger events are Volter Kilpi literature week in July and Salmon market (Lohimarkkinat) in August.

The basic services in the municipality include three groceries, a liquor store, a library and a bank.

The municipality is unilingually Finnish even though it is located adjacent to the Swedish speaking Åland-region.

The municipality is named after King Gustav III of Sweden.