A total of 45 fire fighters battled a blaze at the Chinnor and Princes Risborough Railway this morning.
The fire, which broke out at around 2am, was in a 1930s train carriage which was due to be restored.
Using high and low pressure water jets firemen were able to prevent the fire from spreading to a nearby carriage and rolling stock.
A cause for the fire is not yet known but arson has not been ruled out. No one was injured in the fire.