The authors developed a golf swing skill evaluation system using 3-axis piezoresistive accelerometers. Three different kinds of 3-axis piezoresistive accelerometers were attached on the golfer's hip, left wrist and the golf club head. The acceleration time series from these sensors and the synchronized video images were measured during the golfer's driver swing motion. In this study, we focused on both the sway motion of the golfer's trunk and the uncock timing during the down swing phase. This application enables golfers to understand their skill characteristics and improve their technique right after their trials.