The Spiez–Zweisimmen railway is a single-track standard-gauge line in Switzerland that is currently operated by BLS AG.

It was formerly owned by the Spiez-Erlenbach-Zweisimmen-Bahn (SEZ), also called the Simmentalbahn (Simme Valley Railway).

It is marketed as part of the GoldenPass Line between Lucerne and Montreux, which also includes the metre-gauge Brünig Railway and Montreux–Lenk im Simmental line and part of the standard-gauge Lake Thun Railway.

The SEZ was formed on 1 January 1942 from the merger of the Spiez-Erlenbach-Bahn (SEB), which opened the line from Spiez to Erlenbach on 16 August 1897, and the Erlenbach-Zweisimmen-Bahn (EZB), which opened the line from Erlenbach to Zweisimmen on 31 October 1902.

In Zweisimmen there is a connection to the narrow-gauge Montreux–Lenk im Simmental line of the Montreux Oberland Bernois Railway (MOB), which runs from Lake Geneva to Lenk im Simmental.