Abstract: Objective To investigate the effect of siRNA-mediated silencing metadherin (MTDH) gene on apoptosis of bladder cancer cells and its mechanisms. Methods RT-PCR and Western blot were used to detect the expression of MTDH mRNA and protein in bladder epithelial immortalized SV-HUC-1 cells and human bladder cancer BIU-87 cells. MTDH gene was targeted silenced by liposomal transfection of MTDH-siRNA, and the silencing effect of MTDH and expression of B cell lymphoma/leukemia -2 gene(Bcl-2), Bcl-2 related X protein (Bax), p53 and phosphorylated Akt (p-Akt) were detected by RT-PCR and Western blot. The effect of MTDH gene silencing on apoptosis of BIU-87 cells was detected by flow cytometry. Results The mRNA and protein expressions of MTDH gene in human bladder cancer BIU-87 cells were significantly higher than those in bladder epithelial immortalized SVHUC-1 cells (0.82±0.05) vs (0.25±0.03), (0.42±0.06) vs (0.18±0.05); P< 0.05, respectively. Compared with NC group, the mRNA and protein expressions of MTDH2 in cells of siRNA MTDH2 group and their expressions of MTDH3 in cells of siRNA MTDH3 group decreased significantly MTDH2: (0.31±0.03) vs (1.02±0.03), (0.29±0.02) vs (0.48±0.05); MTDH3: (0.22±0.05) vs (1.02±0.03), (0.18±0.08) vs (0.48±0.05); all P< 0.05, and the decrease in siRNA MTDH3 group was greater than that in siRNA MTDH2 group; While, there was no significant difference between siRNA NC group and siRNA MTDH1 group (P> 0.05).After silencing of MTDH, compared with NC group, the apoptosis rate of BIU-87 cells (38.86%±2.52%) vs (9.95%±1.26%), p53(1.58±0.07) vs (0.61±0.04) and Bax protein (0.86±0.06) vs (0.43±0.03) in siRNA MTDH group were significantly higher, while p-Akt protein (0.31±0.03) vs (0.75±0.08) and Bcl-2 protein (0.35±0.08) vs (1.26±0.12) decreased significantly, and the differences were all statistically significant (all P< 0.05), but the difference between NC group and siRNA NC was not significant(P> 0.05). Conclusion MTDH gene silencing may induce apoptosis of BIU-87 cells by up regulating the expression of p53, Bax protein and down regulating the expression of p-Akt, Bcl-2 protein.