Objective: Oxidant/antioxidant balance has been suggested as an important factor for initiation and progression of cancer. The purpose of this study was to examine 8-hydroxy-2'-deoxyguanosine (8-OHdG) level which is a marker of oxidative DNA damage, superoxide dismutase (SOD), glutathione peroxidase (GPx) and glutathione S-transferase (GST) activities as antioxidant enzymes, in serum of urinary bladder cancer, and to determine relations between measured parameters and tumor characteristics such as histological grade, local invasion and tumor size. Material and Methods: Forty patients with urinary bladder cancer were included in the study. Blood samples were collected just before the resection. Serum levels of 8-OHdG were measured with a competitive ELISA kit, SOD and GPx activities were measured by spectrophotometric kits, GST activity was determined by spectrophotometric assay. Results: There was no significant difference between patient and control groups for serum 8-OHdG level and GPx activity. However serum SOD activity was significantly lower (P<0.001) and GST activity was significantly higher (P<0.001) in the patient group as compared to control group. Tumor size found to be negatively correlated with GST activity (r: -0.43, P < 0.01). Conclusion: Data show that serum level of 8-OHdG does not have a prognostic potential for urinary bladder cancer. Antioxidant balance is disturbed in these patients however changes in antioxidant enzyme activities does not have a prognostic value. The most promising antioxidant enzyme is GST because of its negative association with tumor size.