Abstract: The present invention discloses an optical sensing system which uses a plurality of positioning holes to identify the positions of corresponding encoding holes so that an encoding signal can be accurately generated according to each detected positioning hole and all the corresponding encoding holes. The optical sensing system comprises an optical panel having a plurality of encoding holes and positioning holes, a sensing device for detecting movements of the optical panel related to the sensing device, and a control circuit connected to the sensing device. The sensing device comprises a light source for emitting light to the optical panel, a first light detector for detecting the light transmitted through the positioning holes and a second light detector for detecting the light transmitted through the encoding holes. The control circuit converts an output of the second light detector into an encoding signal when one of the positioning holes is detected by the first light detector.