Introduction: The Inertial Measurement Unit (IMU) is electronic device that enabled us to record joint angles, gait event and spatiotemporal parameter using accelerometers. IMU contain sensors known as inertial sensor which measures its movement by using the inertia principle. This study aimed to determine validity and reliability of spatiotemporal gait parameter using the IMU sensor. Methods: This study are prospective cross-sectional recruited thirteen convenience subjects (four men, nine women; 50.0 +/-15.0 years) diagnosed with chronic Non-Specific Lower Back Pain (LBP) from Physiotherapy Department, upon an Orthopedic Specialist’s referral, at Hospital Sultanah Aminah Johor Bahru. Spatiotemporal parameters interested: left and right velocity, cadence, stride/step time and stride/step length recorded by Vicon system and IMU sensors synchronously. Results: Higher validity was indicated at the Trial 2 detected by the IMU sensors comparing Vicon system, with significant correlation p ≤ 0.05 except stride time left shank (r = 0.539, p = 0.06) , left foot (r = 0.495, p = 0.11) and step length left shank (r = 0.532, p = 0.06). The result of study also indicated that the reliability of the IMU sensors based on ICCs ≥ 0.75 and 95% CI 0.180 – 0.993, p ≤ 0.01 in Non-specific LBP patients for spatiotemporal gait parameters comparing Trial 1 and Trial 2. Conclusion: The IMU system performs to be valid and reliable for determine spatiotemporal gait parameters in Non-specific LBP patients. IMU provides a possible solution to measure spatiotemporal gait in a clinical setting without requiring specific working area and professional technician.