| Kuusisto Castle | |
| Native Name: | Finnish: Kuusiston piispanlinna Swedish: Kustö biskopsborg |
| Building Type: | Medieval castle |
| Location: | Kaarina, Finland |
| Address: | Linnanrauniontie 633 FI-21620 Kaarina Finland |
| Coordinates: | 60.4078°N 22.4747°W |
Kuusisto Castle (fi|Kuusiston piispanlinna, sv|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, although the site seems to have been a bishop's residence by the 1290s.
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.