Background: Manganese (Mn) is one the more important trace elements in the humans. Mn plays an important role in antioxidant defences and it is an essential cofactor for a number of enzymes. Some studies have revealed that Mn deficiency is teratogenic. The relationship of Mn deficiency and cancer induction also has been studied in some studies. We evaluated the serum Mn concentration in patients with bladder cancer in comparison with healthy individuals. Methods: During this cross sectional study, 51 patients with bladder cancer and 58 normal subjects were selected regarding the inclusion and exclusion criteria. Blood samples were collected after 8 hours of fasting. The Mn serum concentration was measured in all samples and copamared between two groups. Findings: Mean of serum Mn concentration was 1.3 ± 0.39 µg/l in bladder cancer patients and 1.87 ± 0.84 µg/l in control group. There was a significant difference between two groups (p < 0.001). Conclusion: According to the results of this study Mn serum concentration had significant decrease in bladder cancer patients in comparison with normal subjects. This result is similar to the other researches done in different cancers. Regarding the high Mn level in fresh foods and vegetables, consumption of these nutrients, is recommended in high risk individuals for bladder cancer. Key words: Bladder cancer, trace elements, manganese.