Zwieselberg is a former municipality in the administrative district of Thun in the Canton of Bern in Switzerland . On 1 January 2024 the former municipality of Zwieselberg merged to form the municipality of Reutigen .

Zwieselberg is first mentioned in 1345 as der Zwiselberg.

The oldest trace of a settlement in the area are a Bronze Age ruin at Bürgli and a grave at Bühl. A small Roman settlement was built on the ruin at Bürgli. The Romans also built a lime kiln at Chalchmädere.