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Wearable joint kinematics monitoring is effective for analyzing daily human behavior, for evaluating the knee functionality in the daily life, etc. This study proposes a new wearable joint kinematics monitoring system using a composite sensor which is composed of inertial and magnetic sensors. For each segment of the joint, the composite sensor is attached. By indentifying the two sets of acceleration and magnetic vector at the center of knee joint, difference of pose between the sensors are estimated. And, all of three joint angles; flexion/extension (f/e) angle, internal/external (i/e) rotation angle and varus/valgus (v/v) angle, are calculated. The proposed system was applied to knee joint kinematic analysis. The measurement accuracy was evaluated by comparing with optical sensor system. The mean error of measuring f/e angle was -1.61 plusmn 3.09 deg; of measuring i/e angle was 0.93 plusmn 1.75 deg; and of measuring v/v angle was 1.83 plusmn 1.79 deg. To demonstrate the applicability of wearable monitoring, the proposed method was applied to measure knee joint angles during walking and during stair-climbing.