Gearboxes are the most commonly used transmission system, which can provide desired speed and torque from a rotating power source to another device. Time-varying mesh stiffness (TVMS) is one of the major causes of vibration and noise in the gear transmission system. In this work, TVMS analysis was carried out on healthy as well as faulty spur gear pairs to see the difference in healthy and faulty condition. The variation of TVMS under fault is found to be different than that under normal condition. Thus, TVMS analysis is found to be useful for diagnosing faults in a gear pair.