The aim of this study is to investigate the effects of epilepsy, valproic acid and oxcarbazepine on nitric oxide levels, lipid peroxidation and xanthine oxidase levels in newly diagnosed epileptic children and healthy controls. A total of 49 patients with newly diagnosed idiopathic epilepsy and 15 healthy children were enrolled in this study. Of these 49 patients, 16 children were treated with valproate and 16 treated with oxcarbazepine. Nitric oxide, malondialdehyde and xanthine oxidase levels prior to antiepileptic drug therapy were measured in the serum. Blood samples were drawn before antiepileptic drug therapy and after 3 and 6 months of the antiepileptic drug treatment. Nitric oxide levels were statistically higher in the newly diagnosed epileptic patients. In oxcarbazepine group, the nitric oxide and malondialdehyde levels were found to be decreased. No statistically significant differences were noted in nitric oxide, malondialdehyde and xanthine oxidase levels in valproic acid treated group. Oxcarbazepine which is a frequently used new antiepileptic drug in childhood epilepsy may modify nitric oxide levels and lipid peroxidation. These results suggest that decreased lipid peroxidation would play a role in the mechanism of antiepileptic effects by oxcarbazepine treatment. © 2010 British Epilepsy Association.