An encoder module adapted for a robotic arm is provided and includes a bracket, a bearing embedded in the bracket, an adaptor ring embedded in the bearing, a circuit board fixed on the bracket and an encoder plate. The bracket includes a ring-shaped structure. The adaptor ring includes a ring-shaped flange portion and a protruding portion. The protruding portion is located adjacent to an inner periphery of the ring-shaped flange portion and protrudes from the ring-shaped flange portion. An outer periphery and an inner periphery of the bearing engage with an inner periphery of the ring-shaped structure and an outer periphery of the protruding portion respectively. The circuit board includes a detector. The encoder plate is fixed on the ring-shaped flange portion and located at a position corresponding to the detector and between the detector and the adaptor ring. The encoder module has less accumulated error and improved accuracy.