The development of the EEG background activity is generally impaired in children with epilepsy. Antiepileptic drugs (AEDs) are one of the important factor which influence the EEG background activity. We studied the effect of AEDs on the EEG. Subjects were 46 normal children and 48 children with epilepsy aged 5 to 15, who had not any organic brain damage and showed normal psychomotor development. Forty children with epilepsy (CBZ; 30 cases, VPA; 10 cases) had been on monopharmacy and 8 cases on polypharmacy. All of them have outgrown their epilepsy. The serial EEGs were recorded during withdrawal and after discontinuation of AED in each patient. These records were evaluated using computerized power spectral analysis. CBZ reduction associated with a decrease in delta and theta powers and an increase in alpha-2 power, which were also observed at VPA reduction in concomitant AEDs (VPA+CBZ). No parameter changed by VPA reduction in monopharmacy. The slowing of the EEG background activity was noticed even after discontinuation of CBZ. It required more time after discontinuation of CBZ in younger children than older before the EEG background activity became normal controls. These findings suggested that CBZ had a adverse effect, which was more remarkable in younger children than older children, on the development of EEG background activity and that the effect of CBZ on EEG was different from that of VPA.