Robotic surgery in the head and neck areas can help in keeping the safety margin to critical organs and performing minimally invasive surgery. This work proposes an ear surgery robot to perform an automatic mastoidectomy. Using the temporal bone model based on a patient's CT image, the best position and orientation of a drill hand piece are determined and recorded. After registration of the image coordinate into the robot coordinate, the robot re-plays the surgical procedure performed by the surgeon. In phantom studies, a fine agreement could be observed between the human surgery and the robot surgery.