Objective To investigate the electromyographic activities of anterior temporalis（TA）, masseter muscle （MM）, digastric anterior（DA）, sternocleidomastoid（SCM） at postural position（MPP） and various mandibular movements in prognathic patients. Methods Thirty-two patients with prognathism were selected from the clinic of oral and maxillofacial surgery of China Medical University. 36 healthy college students with normal occlusion were selected as normal controls. A BioEMG Ⅱ diagnostic system with BioFLEX surface electrode was used to record the electromyographic activities of the above muscles. Results Compared with the control group, the electromyographic activities of TA, SCM and DA in prognathic patients were higher in MPP. The electromyographic activities of TA, MM were significantly lower than the control group in clenching（P
