Siedenburg is a Samtgemeinde ("collective municipality") in the district of Diepholz, in Lower Saxony, Germany. Its seat is in Siedenburg.

The Samtgemeinde Siedenburg consists of the following municipalities:

1. Borstel
2. Maasen
3. Mellinghausen
4. Siedenburg
5. Staffhorst

52°42′00″N 8°55′59″E / 52.700°N 8.933°E / 52.700; 8.933