Abstract： Objective To investigate the gene expression of PIWIL2 in the bladder urothelial carcinoma (BTCC) and siRNA interact on PIWIL2 gene expression in human bladder cancer cell line BIU-87.Methods Semi-quantitative reverse transcription polymerase chain reaction (qRT-PCR) was applied to detect the PIWIL2 expressions in tissues of BTCC (46 cases),cystitis glandularis(21 cases),adjacent non-cancerous tissues (17 cases) and normal bladder tissues (7 cases). 3 specific siRNA targeted PIWIL2 gene were synthesized after designed and transferred. After siRNA was transferred into BIU-87 cells, MTI and TUNEL methods were applied to detect the proliferation inhibitory rate (IR) and apoptosis index (AI) in BIU-87 cells,qRT-PCR and Western blot were used to examine effects of siRNA on the expressions of the PIWIL2 gene and protein,respectively.Results The expression rate of PIWIL2 mRNA in BTCC tissues was 76.08 ％(35/46) and significantly higher than those in the cystitis glandularis tissues (42.86 ％,9/21),adjacent non-cancerous tissues (41.17 ％,7/17) and normal tissues (7.14 ％,1/14) (P =0.008,P =0.010,P =0.000).The IR [(37.52±8.84) ％,(64.36±9.64)％] and (62.94±8.43) ％] and AI [(26.18±5.42) ％,(38.75±6.19) ％ and (40.02±5.64) ％] of BIU-87 cells in the siRNA 1～3 groups were respectively significantly higher than those [(1.97±0.02) ％ and (3.35±0.47) ％] in the control group(P=0.000),and expressions of PIWIL2 mRNA and protein in the siRNA groups were both lower than those in the control group. Moreover, the effects of siRNA 2 group and siRNA 3 group on inhibiting PIWIL2 expression, IR and AI of BIU-87 cells were stronger than siRNA 1 group. Conclusion The over-expression of PIWIL2 suggested that it played an important role in the mechanism of development and malignant progression of BTCC. The siRNA of transcription can significantly inhibit its expression, induce cell apoptosis and inhibit the growth of BIU-87 cells which might provide the experimental evidence for the gene targeting therapy of bladder tumor.