Alt-Signau Castle (German: Ruine Alt-Signau) is a ruined castle in the municipality of Bowil in the canton of Bern in Switzerland.

The castle was the ancestral home of the Barons of Signau.

The family was first mentioned in 1130 when Werner von Signau appeared in a historical record.

The castle was designed to protect and control the road between the Emmental and the Aare river.

Media related to Ruine Alt-Signau at Wikimedia Commons