Objective: This study was aimed to analyze the serum total antioxidant/total oxidant (TAS/TOS) levels and thiol/ disulphide balance of children with autism spectrum disorders (ASD) and draws a comparison with those of healthy children. Methods: The study involved 46 children diagnosed with ASD, along with 45 healthy children. The developmental stage, degree of intelligence and autism symptom severity of the ASD group were assessed using the Autism Behavior Checklist (ABC), Problematic Behavior Control List (PBCL), Childhood Autism Checklist Scale (CARS) and developmentally appropriate screening or IQ tests. Clinical, sociological and demographic data were obtained for both groups. The TAS/TOS levels and thiol/disulphide balance of both groups were analyzed and their oxidative stress index was obtained from the formula TAS/TOSx100. SPSS 17.0 was used for statistical analyses. p [Anadolu Psikiyatri Derg 2018; 19(3.000): 314-322]