Abstract: Objective To investigate the expression of microRNA-138（miR-138）in bladder cancer T24 cells and to study its effect on proliferation and apoptosis of bladder cancer cells as well as its possible target genes. Methods Real-time quantitative PCR（QPCR） was used to detect the expression of miR-138 in bladder cancer cell line T24 and normal bladder epithelial cells SV-HUC-1. T24 cells were divided into normal control group，miR-138 negative control group and miR-138 transfection group, which were transfected with none, negative control fragment and miR-138 mimics. MTT assay and flow cytometry were performed to determine the effect of miR-138 on cell proliferation and apoptosis. Western blotting was used to detect silent mating type information regulation 2 homolog 1（SIRT1）protein levels in each group. Dual luciferase reporter assay was used to confirm the target relationship between miR-138 and SIRT1. Results The level of miR-138 in bladder cancer T24 cells was 0.57±0.19，lower than 1.00±0.26 of normal bladder epithelial cells，and the difference was statistically significant（P＜0.05）. The miR-138 level of miR-138 transfection group was 2.59±0.67，higher than 1.00±0.36 of normal control group and 1.08±0.49 of miR-138 negative control group（P＜0.05）. The proliferation rate of miR138 transfection group was lower than that in miR-138 negative control group and normal control group with statistical significance（P＜0.05）. Fortyeight hours after transfection，the apoptotic rate of miR-138 transfection group was（29.8±1.9）％，higher than（5.8±1.2）％ of normal control group and（7.7±0.9）％ of miR138 negative control group（P＜0.05）. The relative expression of miR138 in miR-138 transfection group was 0.59±0.22，lower than 1.00±0.35 of normal control group and 1.20±0.42 of miR-138 negative control group（P＜0.05）. The double luciferase reporter assay further confirmed that SIRT1 was a direct target of miR138. Conclusion MiR-138 is decreased in bladder cancer cells，and the over-expression of miR-138 may inhibit the proliferation and promote apoptosis of bladder cancer cells by targeting SIRT1.