Objectives：This study was designed to detect the expression of Mel-18 in human bladder urothelial tumors, and to investigate the correlation between Mel-18 expression and age, gender, tumor size, tumor amount, tumor grade and stage of patients with bladder urothelial tumors. Methods：Immunohistochemical staining with Mel-18 specific antibodies was performed on 71 paraffin samples of human bladder urothelial tumors in Gulou Hospital between August 2008 and August 2009. All staining results were evaluated in a semiquantitative way, and data were analyzed using chi-square analysis or Fisher exact probabilistic method. Results： Staining was observed in scellular nucleus of some bladder urothelial tumors, the positive rate of Mel-18 expression in 71 patients was 33.8%. The positive rate of Mel-18 expression was 40.4% in the bladder urothelial tumors with size smaller than 3cm, and 7.1% in the tumors with size larger than 3cm, with significant difference(P<0.05). It was significantly lower in high-grade bladder urothelial carcinoma than in PUNLMP and low-grade bladder urothelial carcinoma(10.8% vs 75.0%, P<0.001;10.8% vs 53.8%,P<0.001). It was significantly lower in bladder urothelial carcinoma with clinical stage T1 than Ta(P<0.001). No correlation was found between Mel-18 expression and age, gender, or tumor amount. Conclusions：The expression intensity of Mel-18 was correlated with tumor size, classification and T stage. As a tumor suppressor, the expression of Mel-18 showed potential significance in clinicopathological diagnosis of human bladder urothelial tumors.