The aim of this study was to examine the effects of neosporosis on the oxidative stress cow naturally infected with Neospora caninum. Ten infected cow with Neospora caninum and ten healthy were included in this study. The neospora infection was diagnosed in the cows by using a commercially available competitive enzyme-linked immunosorbent assay kit. Compared with healthy controls, levels of malondialdehyde and serum concentration of nitric oxide metabolites higher in the infected group. Furthermore, total antioxidant activities were found lowered in the infected group compared to the control group. The results demonstrated that oxidative stress markers are greatly increased in cows naturally infected with Neospora can mum.