The derelict buildings at the Old Cruicksank School between Wallyford and Whitecraig were spotted burning just before 6pm on Wednesday.
Firefighters found the building well-alight on arrival and three appliances were called to tackle the blaze.
Police had to close the A6094 briely to allow firefighters access to a hydrant, but while there was heavy smoke drifting over the area there were no reports of injuries.
A height appliance was called to use as a water tower in order to cool the building. The incident was still ongoing at 10.30pm last night.