| Alt-Signau | |
| Native Name: | Ruine Alt-Signau |
| Built: | about 1130 |
| Type: | hill castle |
| Condition: | Ruined walls |
| Location: | Bowil |
| Occupants: | Freiherren of Signau |
| Coordinates: | 46.9043°N 7.7227°W |
| Map Type: | Switzerland |
| Code: | CH-BE |
Alt-Signau Castle (de|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.In the mid-14th century the castle was abandoned when the family moved to Neu-Signau Castle on a hill across the valley.
The ruin is relatively well preserved.