The Bellinzona–Mesocco railway (Italian: Ferrovia Bellinzona–Mesocco; BM) was a Swiss metre gauge railway that linked the towns of Bellinzona, in the canton of Ticino and Mesocco, in the canton of Graubünden. The line was built by the Societa Ferrovia elettrica Bellinzona-Mesocco and later became part of the Rhaetian Railway. Today the section of the line between Castione-Arbedo, and Cama is operated by the Società Esercizio Ferroviario Turistico (SEFT) as a tourist railway known as the Ferrovia Mesolcinese.
The Gotthard railway opened in 1882, providing a transport link to the communities of the valley of the Ticino River. In order to provide a link to the communities of the Val Mesolcina, the Bellinzona–Mesocco railway was opened in 1907. Although intended as a feeder line to the Gotthard railway, the Bellinzona terminus of the BM was located some 500 metres (1,600 ft) from the main line station, and the main transfer point was Castione-Arbedo station further north.
From the beginning, an extension over the San Bernardino Pass to Thusis was planned, in order to provide a rail connection to the Rhaetian Railway (RhB), but this was not constructed. In 1942 the line was merged into the RhB, but it was never connected to that railway's main network. In 1972, all passenger traffic ceased and the line between Bellinzona and Castione-Arbedo was closed, whilst freight traffic continued on the rest of the line.
In 1978 the upper section of the line was damaged by a bad storm, and was never repaired. The remnant of the line between Castione-Arbedo and Cama continued carrying freight traffic until the closure of the factories on the line removed that traffic. In 2003, freight traffic ceased and the line was transferred to SEFT.
The original line was 31.3 kilometres (19.4 mi) long, and was electrified at 1500 V DC using overhead lines. It had 17 stops, a maximum gradient of 6% and a minimum radius of 80 metres (260 ft). The surviving tourist line is 12.7 kilometres (7.9 mi) long.