Wrist angular velocity assessment is important for assessing the risks in hand-intensive work. This study compared the measurement accuracy of an inertial measurement unit (IMU)-smartphone system, an electronic goniometer and an optical tracking system (OTS) for measuring wrist flexion velocity. Six participants performed three sets of standard hand/wrist movements and three simulated work tasks. The results showed the IMUs had adequate accuracy comparing to the OTS during standard movements of low to medium pace. The accuracy of the IMUs compared to the OTS was lower during fast pace movements and simulated work tasks. Still, the IMUs had in general small differences compared to the goniometer in flexion/extension and simulated work tasks. Therefore, the IMU system may be used by researchers and practitioners for assessing wrist flexion velocity in hand-intensive work. Future studies need to explore algorithms to improve the IMU-smartphone system and reduce errors.