The integration of sensing and communications (ISAC) has brought considerable benefit in predictive beamform?ing. However, it is dedicated to the line-of-sight channels, and the effect of the spatial degree of freedom (DoF) of multipath channels on ISAC performance has not been revealed thus far. This compact letter proposed a novel ISAC-assisted beam?tracking solution in multipath channels. Based on the reflected echoes, the kinematic parameters are measured and the extended Kalman filtering (EKF) is designed for angle prediction. The fine beam tracking method is also proposed based on the tracking results of the EKF. Simulation results show that the proposed method has a remarkable superiority over the conventional feedback-based one. In addition, the angle parameters observed from radar echoes are not always the optimal alignment direction, which still has nearly a one-third gap from the global optimal performance in a strong multipath environment, and this gap can be bridged by the proposed fine beam tracking method.