OBJECTIVE: The event related potential (ERP-P300) is useful to determine cognitive disturbances. This study examined the changes of ERP-P300 following different dosages of topiramate (TPM) treatment in children with epilepsy in order to investigate the effect of different dosages of TPM on cognitive function. METHODS: Thirty cases of benign childhood epilepsy with centrotemporal spikes (BECTS) were first administered with TPM at a dosage of 2 mg/kg?d for 6 months. Afterwards they received another 6 months of TPM treatment at a dosage of 5 mg/kg?d. ERP-P300 was tested before and after different dosages of TPM treatment. RESULTS: There were no significant differences in the latency and amplitude of ERP-P300 before and after 6 months low dosages of TPM treatment. However, the latency was more prolonged and the amplitude was reduced in the ERP-P300 testing after 6 months high dosage of TMP treatment (P<0.01). CONCLUSIONS: The effect of TPM on cognitive function is related to its dosage in children with epilepsy.