The Rheineck–Walzenhausen mountain railway (German: Bergbahn Rheineck–Walzenhausen; RhW) is a 1.9 kilometres (1.18 mi) long rack railway in Switzerland. It links Rheineck station, in the municipality of Rheineck and the canton of St Gallen, with the village and health resort of Walzenhausen, in the canton of Appenzell Ausserrhoden . Passenger service on the line now forms part of the St. Gallen S-Bahn, branded as the S26. The S26 is also part of the Bodensee S-Bahn.

The line is owned and operated by the Appenzell Railways company, which also operates several other railway lines in the two Appenzell cantons.