A shaft ground ring and an assembly thereof are disclosed. According to the present invention, there is provided a shaft ground ring fastened to a shaft of an electric motor to prevent electrical erosion caused by a leakage current, the shaft ground ring including a ring body formed to extend to surround an outer circumferential surface of the shaft and a plurality of ground protrusions formed to protrude from an inner circumferential surface of the ring body, being in contact with the outer circumferential surface of the shaft, and disposed to be spaced a predetermined gap from each other along the ring body. The present invention maintains a proper ground state in an oil cooled environment and thus can properly function a high-capacity electric motor.