The occlusal plane was designed as parallel to Camper's line (the standard dentures) and 5 degree inclined upward, downward laterally and anterior-posterior for comparing the activities of masticatory muscles. Following results were obtained: (1) the amplitude of the masseter (Mm) and the anterior temporalis (Ta) muscles with standard dentures biting in intercuspal position were the highest among those with other dentures, (2) during unilateral chewing with standard dentures, the average amplitude of the anterior digastric muscles (Da) on the balanced side was higher than that on the working side, but the amplitude values of the Mm and the Ta on the working side were significantly lower than those on the opposite side, (3) to incline the plane forward or backward may cause the activity of the Da increased in the balanced side and (4) to incline the plane right or left the amplitude of Ta and Mm between the working and the balanced side was not significant different.