A mouse motion trajectory testing system includes a testing fixture and an electronic calculator connected to the testing fixture. The testing fixture includes a testing base, a rotatable member under the testing base, and a controlling unit. The testing base is used for fixing the tested mouse thereon. The controlling unit is used for driving the rotatable member to be rotated for a preset number of revolutions at a preset speed, so that the tested mouse generates a motion signal. The electronic calculator has testing program for receiving the motion signal from the tested mouse, thereby judging whether the tested mouse is qualified or not.