The Taff Vale Railway O4 class was a class of 0-6-2T steam tank locomotives designed by Tom Hurry Riches and introduced to the Taff Vale Railway in 1907.

They were rebuilt with taper boilers and superheaters by the Great Western Railway (GWR) from 1924.

The last three locos, 290, 317 and 321 were withdrawn together from Cardiff East Dock shed in July 1955.

The locomotives were built in several batches by Vulcan Foundry, Manning Wardle and Beyer, Peacock and Company.

This article relating to steam locomotives operated in the United Kingdom is a stub.