SenseChair, an office-chair-shaped body motion sensor, enables to detect body sway of a sitting user by its embedded four pressure sensors. We have studied the possible utility of a novel method to assess the “ensembility” among multiple sitting players on multiple SenseChairs. In this study, we examined the relationship between the ensembility of three players and evaluation for their music performance. Results showed that performance high in ensembility received a higher evaluation. The possible necessity of further study was discussed.