Huvudsta gamla slott, Historical building in Solna Municipality, Sweden

Huvudsta gamla slott is a one-storey wooden building from 1750, moved in 1834 to a slope above Ulvsundasjön, about 300 metres northwest of Huvudsta gård in Solna. Its exterior retains the original windows, doors and profiled mouldings, while the interior was divided into four family flats. The preschool run by the Swedish Church left in summer 2018.

Built in 1750, the structure became notorious when Count Claes Horn and associates plotted King Gustav III's assassination there in 1792. The building was relocated to its present location in 1834 when Russian ambassador Peter van Suchtelen planned to construct a new main building.

The house is known as "Mördarslottet" (the Murder Castle) because tradition holds that Count Claes Horn, Jacob Anckarström, Carl Fredrik Pechlin and Adolph Ribbing met here in 1792 to plan the assassination of Gustav III. The name Huvudsta derives from the old farm name Hufvudsta.

The building stands on a wooded slope about 300 metres northwest of Huvudsta gård, on the north side of Ulvsundasjön. It is not open to the public; the preschool run by the Swedish Church closed in summer 2018. Visitors can walk around the exterior and see the preserved window and door mouldings.

The 17th-century painted wooden ceiling found in the attic during the 1960s restoration shows a floating cherub and the Stenbock coat of arms in grey tones. It was remounted in the entrance hall, where visitors can see it.