Abstract: In this study, we evaluate the changes on the Events-Related Potentials (ERPs) of P300 in patients with asymptomatic cerebral infarction which was detected by Magnetic Resonance Imaging (MRI). We examined 37 patients who visited University Hospital with complaint of headache or dizziness which had no episodes of stroke nor any neurological defect including obvious dementia between March 1988 to March 2000. MRI were performed and we found 23 cases of patients showed multiplelacunar infarction and 14 patients (8 male and 6 female) (with average age of 70) showed marked leuko-araiosis or periventricular high intensity with or without lacunar infarction in T2-weight image. We compared these two group with 13 healthy age-match (7 male and 6 female with average age of 68) as control group. ERPs was recorded with a band-pass filter of 0.01-120 c s-1. ERPs were derived from the Fz, Cz and Pz referenced to linked earlobe electrode and mini-mental test were performed in all subject. P300 ERPs were recorded by standard oddball paradigm with the subject seated in a reclined easy chair. In auditory paradigms, during the subject’s eyes were closed, 2,000 Hz tone were used as target and 1,000 Hz tone as none target through headphone. The target tone were presented in a random sequence at the rate of 20%. Then the subjects were instruct to count the number of target tone. Statistical analysis was performed using one factor ANOVA to determine inter-group differences. P300 latency in patients MRI showed multiple lacunar infarction (378.8±33.6 ms) and in patients MRI showed marked leuko-araiosis infarction (388.3±3.6 ms), were significantly prolonged as compare to normal healthy person (338.6±13.5 ms). However, the amplitude of P300 was remain unchanged. The scores obtained from Mini Mental State Test (MMST) were showed no significantly different between the normal elderly and patient with multiple lacunar infarction and in leuko-araiosis infarction patients Comparison the latency and amplitude of N100, P200 and N200 were also no significantly differences. The present finding, we found the P300 latency was significantly prolong in multiple lacunar infarction patients and in leuko-araiosis infarction patients. But there were no significant changes in the amplitude of P300. Thus, we can concluded that cognitive function was impaired with asymptomatic cerebral infarction.