It happened Tuesday morning on the Old Bar Harbor Road.
The owners of the home were not there at the time.
Crews from all four towns on Mount Desert Island, Ellsworth, Lamoine and Hancock were called to help fight the fire.
Bar Harbor Fire Chief Matt Bartlett said "Heavy fire on the first floor the backside of the building and we've been fighting it and trying to get it extinguished."
Officials said they are still trying to determine what may have started that fire.