The present study was undertaken to evaluate the place of oxidative stress on breast cancer. Lipid peroxidation as evidenced by malondialdehyde (NIDA) and the status of the antioxidants superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GPx) were estimated in tissues of 10 fibroadenoma and 40 breast cancer patients. Lipid peroxidation in breast cancer tissues was enhanced compared to nonmalignant tissues (p < 0.001). Similarly, antioxidants SOD (p < 0.001) and GPx (p = 0.007) in tumor tissues significantly were increased. On the contrary, CAT activity was found significantly decreased (p < 0.001). We found that oxidant/antioxidant status was independent from any prognostic factors concerning breast cancer. The results of our study have shown higher oxygen-free-radical production and decreased CAT activity support the oxidative stress hypothesis in breast carcinogenesis.