Diabetes mellitus (DM) leads to a variety of complications and thus we have retrospectively studied to investigate problems of nerve conduction velocity (NCV) study and the heart in the patients with type-II DM. Blood glucose and blood pressure levels were higher in DM group than in Non-DM group. We found that several latencies were delayed in motor conduction study of upper (median and ulnar nerve) and lower extremities (peroneal and tibial nerve), whereas amplitudes and NCVs were decreased in DM group compared with Non-DM group. Latencies of sensory conduction study in upper and lower extremities (sural nerve) were delayed, while amplitudes and NCVs were lower in DM group than in Non-DM group. Abnormal percent of the electrocardiogram was higher in DM group than in Non-DM group. This retrospective study suggests that type-II DM can cause a damage effect on the peripheral nerve and the heart function.