The cognive evoked potential has been used as an objective test of the human cognitive function. The most prominent component of cognitive evoked potential is P3 (also known as the P300) which has been linked in many studies with cognitive function. According to many studies. The latency of P3 corresponds to time involved in stimulus evaluation and categorization. 15 chronic alcoholics and 15 normal controls were studied on the cognitive evoked potential to evaluatt impairment of cognitive function using the auditory stimulus of odd-ball procedure. We measured latencies and arnplitudes of P3 on 20 sites according to the international 10-20 systern for electrode placement, and results were as follows: .1. All latencies of P3 were significantly longer for chronic alcoholics than in norrnal controls on 20 sites. 2. All amplitudes ot P3 were not significantly different between chronic alcoholics and normal controls on 20 sites. 3. P3 arnplitude of chronic alcoholics was highest on Pz, and P4. Fz, C4. F4, and Cz in order. But in normal controls. P3 amplitudes were highest on Fz. And Cz. Pz P4, F4, and C4 in order. With these results, it is suggested that the prolongation of P3 latencies of chronic alcoholics is related to their cognitive impairment.