The aim of this study was to evaluate the electromyographic changes in the anterior temporalis and masseter muscles after fatigue induced by continuous chewing. Surface electrodes were placed bilaterally over the anterior temporalis and masseter muscles of 31 subjects with normal dentition. Recordings were taken every minute from the beginning of chewing to the exact moment the volunteer reported subjective sensation of fatigue in the jaw muscles. The length of endurance period (fatigue threshold) was measured to each subject, as well as the average amplitude and duration of activation phase and duration of relaxation phase through electromyographic recording of each muscle. The average endurance period was about 500 s. No significant change occurred on the average amplitude of activation phase meanwhile the duration of both the activation and relaxation phase diminished after fatigue.281165-7