This paper presents a robotic navigation system for image-guided neurosurgery, which can be applied to the treatment of Parkinson’s disease and biopsy of brain tumor. The system integrates a computer for real-time display of brain anatomy, a magnetic tracking device for measuring the positions and orientations of surgical instruments, and a robot manipulator for guiding surgical instruments to the preplanned positions and orientations. The computer display of brain anatomy offers a convenient tool for surgeons to diagnose brain disease and to plan safe surgical paths; while the tracking device assists the robot manipulator to automatically guide surgical instruments to the preplanned direction. The registrations among the tracking device, the image system, and the robot are completed on the base of coordination mappings of external markers. An experiment of using a skull model for simulating a robotic biopsy of brain tumor has been done to verify the performance of the navigation system. The result shows that the system can accomplish a positioning accuracy around 2 mm.