Abstract: A file guide for use in sharpening a chain saw having a bar, a chain around the periphery of the bar, and a plurality of teeth secured at intervals along the chain, each tooth having a cutting edge at one end thereof constituting its forward end. The file guide comprises a frame adapted to be mounted on the bar of the chain saw, a carriage slidably mounted on the frame for forward and rearward movement relative to the tooth to be sharpened, and a stop carried by the frame for holding the tooth against rearward movement. The carriage has a pair of guide members guiding a file for reciprocation at a predetermined angle relative to the tooth through a cutting stroke of the file for sharpening the tooth at the predetermined angle and a return stroke. The guide members are disposed on opposite sides of the tooth and are spaced longitudinally of the carriage.