Objective: Although pathogenesis of juvenile idiopathic arthritis ( JIA) is poorly understood, it is thought that a triggered inflammation by neutrophil activation due to any reason, released free oxygen radicals and insufficiency of antioxidant system should play role in the chronic course of this disease. In present study, it was aimed to determine the status of oxidant and antioxidant systems in this disease. Methods: In 45 patients with JIA (23 with active disease, 22 on remission), blood samples were taken to determine erythrocyte sedimentation rate (ESR), the serum levels of C-reactive protein (CRP), advanced oxidation protein products (AOPP), myeloperoxidase (MPO), thiol, total oxidant capacity (TOC), total antioxidant capacity (TAC) and neopterin, following physical examination and questioning for current treatments. Results: Serum ESR, CRP, TOC, TAC and, MPO levels were found higher in patients with active disease than those on remission (p<0.05). No difference was found in neopterin, AOPP and thiol levels. Only TOC levels were higher in active phase than remission phase in same patients. Conclusion: Consequently, even data were obtained regarding that oxidant-antioxidant systems were active in JIA patients during active phase in this study; such activation in favor of oxidants was striking. More comprehensive studies are needed to determine whether oxidantantioxidant systems activation is cause or result.