Abstract： Objective To quantitatively measure the masticatory movement and to investigate the change of stomatognathic function in patients with cleft lip and palate.Methods Fifteen patients with complete cleft lip and palate were selected.Electromyography of bilateral anterior temporalis and masseter was measured and mandibular movement was examined during masticatory movement before and after maxillary protraction.Results After treatment,the activity of masticatory muscles in the functional side was increased significantly.In the unilateral mastication side (left) and the right side,the activities of anterior temporalis increased from 45.57(26.75,67.84) mV to 80.24(72.31,91.36) mV and from 45.25(37.34,57.42) mV to 73.56 (59.63,94.80) mV,respectively.In the unilateral mastication side (left) and the right side,the activities of masseter increased from 62.37 (45.76,72.45) mV to 90.35 (78.94,110.45) mV and from 67.53(59.65,80.53) mV to 87.97(72.35,99.79) mV,respectively.No significant increment in the balance side was found during masticatory movement.The masticatory trajectory was not changed significantly.The width of lateral and vertical scale of right side mastication increased significantly (P ＜0.05).Conclusions After the treatment,the activity of masticatory muscles increased significantly,and the width of lateral and vertical scale of right side mastication increased significantly.