To verify validity of a newly developed ultraminiature EMG measurement system (BMS), the ability of BMS to record masseteric EMG was compared with that of a conventional polygraph system (PG) in the daytime. Effective distance between the transmitter unit and receiver unit of BMS was also examined. Subjects were 12 healthy volunteers. During tapping, maximum clenching, and gum chewing of all subjects, distinct bursts were observed in EMG recorded by BMS as well as PG. RMS values of maximum clenching measured by BMS and PG showed a linear and significant correlation, and there was no significant difference between the data of BMS and PG. When distance between the transmitter unit and receiver unit of BMS was 100 cm or less, no artifact signal was observed. Having obtained these findings suggesting ability for precise measurement in the daytime, we are planning to use BMS in home sleep studies in the next step.