The aim of this study was to test the wireless wearable sensor system consists of inertial sensors considering application to rehabilitation. The sensor system was evaluated in measurement of hip, knee and ankle joint angles with healthy subjects comparing to those measured with a 3D motion measurement system. Then, the lower limb joint angles of elderly subjects including paralyzed subjects were measured during gait on the level floor with the sensor system. Evaluation of measured joint angles in comparison with the motion measurement system showed that mean values of the RMSE were smaller than 4 deg for all the joint angles, and mean values of the correlation coefficient were larger than 0.985 for hip and knee joint angles and about 0.90 for ankle joint angle. In measurement with elderly subjects, the sensor system showed some differences in joint angles between the paralyzed and the non-paralyzed sides.