Objective: To assess the cognitive function of epileptic children before and after valproate treatment by use of auditory event-related potentials P300. Methods: 13 patients were tested with auditory event related potentials P300 6 months after treatment. Eight patients were tested after 1-year treatment. Results: there were no statistical differences in the P300 latency, amplitude and reaction time after valproate treatment in epileptic children. Conclusion: There is no significant effect of valproate treatment on the cognitive function of epileptic children.