The flames could be seen from the A34.
Firefighters from Oxford and Kidlington dealt with the fire just before 1am this morning.
The boat was fully engulfed, near to the Trout pub car park in Wolvercote.
It was also spreading to a second boat which was quickly dealt with by fire crews.
Oxfordshire Fire and Rescue says the blaze is 'thought to be suspicious in nature'.
Thames Valley Police is investigating.
Fire crews will be returning to the scene during the day to provide boaters with safety advice.