Grape seed extract (GSE) has been known as being neuroprotective due to its antioxidant properties. The aim of the present study was to examine both the effect of GSE on the penicillin-induced epileptiform activity in rat and the role of nitric oxide (NO) pathway in the effect of GSE. GSE, at doses of 50, 100, 200 mg/kg, significantly decreased the mean frequency of epileptiform activity. GSE, at the highest dose (400 mg/kg), did not change either the frequency or amplitude of epileptiform activity. GSE, at a dose of 200 mg/kg, was the most effective in changing the frequency of epileptiform activity. The occurrence of anticonvulsant activity of GSE was significantly delayed in the presence of selective inducible nitric oxide synthase (iNOS) inhibitor, aminoguanidine (60 mg/kg), which was inhibited by the NO precursor, L-arginine (500 mg/kg). The administration of a non-selective NOS inhibitor, NG-nitro-L-arginine methyl ester (L-NAME) partially reversed the anticonvulsant activity of GSE. Selective neuronal nitric oxide synthase (nNOS) inhibitor, 7-nitroindazole (7-NI) and L-arginine showed a similar anticonvulsant activity in the presence of GSE. The electrophysiological evidence of the present study indicates that GSE decreases the mean frequency of penicillin-induced epileptiform activity, suggesting an anticonvulsant role. iNOS/NO pathway could be involved in mediating anticonvulsant effect of GSE on the epileptiform activity.