A fiducial planar marker is generally used for positional tracking by a single camera. The technology is widely applied to entertainment systems and to medical assistance such as surgical navigation systems. However, the tracking accuracy is not sufficient for precise navigation; therefore, fiducial marker tracking has not replaced position sensors such as infrared light tracking systems. In particular, attitude accuracy is important for tracking because a marker is attached to a convenient position of a tracked tool far from the tool’s tip. Therefore, the attitude error generates a large positional error at the tip. To address this issue, we propose a method of improving fiducial planar marker tracking accuracy by sensor fusion. The proposed tracking system consists of a fiducial marker and a gyroscope, which provides angular velocity. To integrate the sensors, a sensor fusion filter based on a Kalman filter was designed. The feasibility and performance of the filter were validated experimentally by using a three-axis motorized rotational stage with potentiometers. The results showed that the root-mean-square error of attitude measurement was reduced by the proposed integration method. We confirmed that sensor fusion with a gyroscope is feasible for 3D tracking of a fiducial planar marker.