A method of joint angle measurement during gait using wearable sensors for rehabilitation was studied in this paper. The method corrected joint angles measured by gyroscopes using joint angles measured by accelerometers with Kalman filter. Although gyroscopes could measure joint angles, their offset drift caused error in measurement of joint angles. At first, we made up small sensor units consist of a gyroscope and an accelerometer. Then, the method was validated with the developed sensor units in measurement of ankle and knee joint angles of three healthy subjects under walking on short distance pathway and on treadmill for long time. The measured joint angles were compared with reference joint angles measured with optical motion measurement system simultaneously. The result for short distance walking showed low RMS errors and high correlation coefficients (3.19deg and 0.918 for the ankle joint, 2.98deg and 0.993 for the knee joint in average). The result for treadmill walking also showed low RMS errors and high correlation coefficients (3.04deg and 0.960 for the ankle, 4.19deg and 0.994 for the knee in average). Although the measurement accuracy decreased in some of trials of a specific subject because of sensor attachment position, the experimental results suggested that joint angle could be measured with good accuracy independent of measurement period of time, walking speeds and subjects.