Kuusisto Castle (Finnish: Kuusiston piispanlinna, Swedish: Kustö biskopsborg) was a medieval episcopal castle on the island of Kuusisto in Kaarina, Finland, near Turku.

The castle was probably built in the early 14th century[citation needed], although the site seems to have been a bishop's residence by the 1290s.

[citation needed] The castle was ordered to be demolished during the Protestant Reformation in 1528 by the king Gustav I of Sweden.

Excavation and reconstruction work on the remaining ruins began in 1891.

This article about a castle in Finland is a stub.