Aim: To explore the processing mechanism of human brain for orientation conflict with event related potential technique. Methods: Totally 10 un dergraduate students who were studying for Bachelor's degree (six males, 21-24 years) from Capital University of Medical Sciences were enrolled as healthy examinees (after signed the informed consent) to observe the response of human brain for orientation conflict. Paired pictures as visual stimuli (S1 and S2) presented sequentially in the computer screen in front of the subjects. S1 and S2 were the same orientated left (condition 1); paired stimuli were both orientated right (condition 2); Above two conditions were paired state. S1 was orientated left and S2 was orientated right (condition 3); S1 was orientated right and S2 was orientated left (condition 4); Latter two conditions were conflict state. Subjects were required to judge whether S2 was the same orientation to S1 under the four conditions, while event related potentials were recorded on their scalps and stored on a hard disk at the same time of stimulating given by American Neuroscan brain-electricity evoked potential workstation. Mean voltage at different state was compared after disposal with off-line analysis. Res ults: Experimental data of 10 examinees were involved in the analysis statistics. 1 Reaction times of the 4 states (condition 1, 2, 3 and 4) were (577±161) ms, (581±173) ms, (586±100) ms and (594±103) ms with the accuracy of 99%, which had insignificant diference [F (1.9) =8.94, P > 0.05]; [F (1 . 9) =13.87, P > 0.05]. 2 Following the onset of S2, ERP components P100, N170, N200 and P300 were recorded in all conditions while in orientation conflicting conditions, N270 was evoked after an enlarged P100, it was mainly distributed at centra-frontal area. 3 Average wave amplitude was analyzed in the four conditions with double factor analysis of variance: There was no significant difference in the mean amplitude of event related potential components neither between the paired conditions nor the two conflict conditions. The mean amplitudes of P100 at parieto-occipital area and P300 at right frontal area in conflict conditions were significantly more positive than those of in paired conditions. The mean amplitude of N270 at right centro-temporal area exceeded that of at the left in conflict conditions, and the mean amplitude of P300 at left parietal area exceeded that of at the right in match conditions while the asymmetry was absent in conflict conditions. Conclusion: A significantly negative wave -N270 can be elicited after fortified P100 (P1) when the irritative direction is different. Fore head of wave amplitude is huge. The orientation information conflict can induce the production of N270.