Accumulating evidence suggests that oxidative stress induced mechanisms are believed to be associated with the pathophysiology of autism. In this study, we recruited 19 Omani autistic children with age-matched controls to analyze their plasma and serum redox status and the levels of ATP, NAD[superscript +] and NADH using well established spectrophotometric assays. A significant decrease was observed in the levels of plasma total antioxidants (TA), reduced glutathione (GSH), superoxide and catalase activity in Omani autistic children as compared to their age-matched controls. In contrary, the level of plasma glutathione peroxidase (GSH-Px) was significantly increased in autistic children. Reduced serum NAD[superscript +] and ATP levels and lower NAD[superscript +]:NADH ratio were observed in patients with autism compared to controls. Finally, a significant inverse correlation was observed between plasma GSH, SOD, catalase activity, and serum NAD[superscript +] and ATP levels, and autism severity using Childhood Autism Rating Scale (CARS) scores. The levels of plasma GSH-Px and serum NADH correlated strongly with autism severity whilst no significant correlation was observed for plasma TA. Our data suggests that increased vulnerability to oxidative stress in autism may occur as a consequence of alterations in antioxidant enzymes leading to mitochondrial dysfunction. (Contains 1 figure and 1 table.)