The purpose of this study was to investigate the duration of the silent period of the masseter muscle in normal subjects after experimental bruxism. The material for this study consisted of 9 male subjects with an age range of 22-24 years who showed normal occlusion clinically and were free from any history or symptoms of temporomandibular joint dysfunction. A jaw-jerk was stimulated by tapping the mandibular symphysis during maximal voluntary clenching with a solenoid-driven hammer. And three separate silent period records were made from the left masseter muscle at the following times: at normal state, after experimental bruxism, 1 week after bruxism. The following conclusions were obtained: 1. The average value of the duration of masseteric silent period during maximal voluntary clenching was $33.62{pm}1.86msec$ when tap force of approximate 650g was applied at normal state. 2. After experimental tooth grinding for 30 minutes, the duration of masseteric silent period increased to $46.29{pm}4.40msec$. 3. Comparing the duration of silent period measured at normal state with that measured after 1 week, the duration of silent period showed reproducibility.