Objectives: Free radicals have been implicated in the pathophysiology of some psychiatric disorders. To examine the role of free radicals in the etiopathogenesis of obsessive-compulsive disorder (OCD), we aimed to assess whether the antioxidant vitamins (E, C and A) activity and malondialdehyde (MDA) levels were associated with OCD. Methods: 48 OCD patients diagnosed according to DSM-IV and 48 healthy volunteers as control group were included in this study. Serum levels of vitamin E and A were determined using RP-HPLC, whereas vitamin C was estimated by phenyl-hydrazine spectrophotometric method. MDA level was measured using UV-VIS spectroscopy. Results: Significant differences in serum vitamin E and C levels were observed between the OCD and control groups (p<0.05). MDA levels were found significantly higher in OCD subjects (p<0.05). Conclusion: Our study found an overall imbalance in antioxidant vitamins level in OCD patients, which may have potential role in etiopathogenesis of the disease process (German J Psychiatry 2012; 15 (1): 10-14).