The Otira Tunnel is a railway tunnel on the Midland Line in the South Island of New Zealand, between Otira and Arthur's Pass. It runs under the Southern Alps from Arthur's Pass to Otira – a length of over 8.5 kilometres (5.3 mi). The gradient is mainly 1 in 33, and the Otira end of the tunnel is over 250 m (820 ft) lower than the Arthur's Pass end.

The Midland line is a 212 km section of railway between Rolleston and Greymouth in the South Island of New Zealand. The line features five major bridges, five viaducts and 17 tunnels, the longest of which is the Otira tunnel. It is the route of the popular TranzAlpine passenger train.