Södertuna (Swedish pronunciation: [sœdɛˈʈʉ̂ːna])[1] is a medieval castle located on a small island in Lake Frösjön in Gnesta Municipality, Sweden.

It has belonged to members of several families: Sparre, Lovisin, Palmenfelt, Ehrensvard, Wachtmeister, Adelborg, and von Eckermann.

The castle and the park were split off in 1985 by the von Eckermann family.

The new owners, together with an additional couple of Norwegian investors, made the palace into a hotel and conference center, which was inaugurated in 1986 by Princess Christina.

In 2007 the castle was sold to the Åström family, which also operates Dufweholms Manor Inn and Gripsholm.