The determination of motor nerve conduction velocity is an important part to electrodiagnosis. Its value as neurophysiologic investigative procedure has been known for many years, and recently it has been utilized as a chinical diagnostic technic. Its most valuable role is differentiating between those conditions which affect the axon primarily and those which affect the anterior horn cell. Many factors such as temperature in the vicinity of the nerve, diameter of the axon, degree of myelinization, age of the patient, local environment of the nerve and intensity of electrical stimulation have been demonstrated to affect the rate of propagation of impulses along motor fibers. Pathologic conditions affecting the axon usually alter the excitability along involved segments and, therefore, result in reduced conduction velocity. The purpose of this study was to determine the normal data of the motor nerve conduction velocities of median, ulnar, tibial and peroneal nerves in Korean. 1. The motor nerve conduction velocities of median, ulnar, peroneal and tibial nerves were 61.54±6.95 (46.7–94.2) m/sec, 61.74±7.28 (45.6–95.0)m/sec, 48.80±5.54 (38.8–69.9) m/sec, 47.39±4.85 (36.2–64.2 m/sec respectively. 2. The condition velocity in the upper extremities has been found 13.5 m/sec faster than in the lower extremities. 3. A significant decline in motor nerve conduction velocities was noted in the over 60 year old age group. 4. There were significant differences between the sexes.