Abstract: Objective: To investigate the impact of diabetes mellitus (DM) on the risk of developing urinary tract tumors. Methods: Two-sample Mendelian randomization (MR) analyses were conducted using summary statistics from the IEU OpenGWAS and FinnGen databases. Phenotypic validation was conducted using crosssectional population analysis, and secondary MR analysis was performed to enhance the strength of evidence. Results: Preliminary MR analysis revealed a weak association between type 2 diabetes mellitus (T2DM) and bladder cancer (OR=1.001, 95% CI: 1.000-1.001, P=0.010). DM (OR=1.016, 95% CI: 1.001-1.032，P=0.037) and T2DM (OR=1.002, 95% CI: 1.001-1.002, P=0.021) were confirmed as risk factors for prostate cancer (PCa), with the findings supported by secondary MR, and were validated by cross-sectional analysis. Subgroup analysis showed that T2DM increased the risk of PCa in situ (OR=2.114, 95% CI: 1.062-4.240, P=0.032). Conclusion: T2DM increases the risk of PCa, especially for carcinoma in situ.