Objective To investigate the expression of miR-216a-5p in various bladder cancer cell lines and regulation of PAK2 gene on the proliferation and apoptosis of bladder cancer cells.Methods The expression of miR-216a-5p in normal bladder cell line SV-HUC-1 and bladder cancer cell lines (5637,J82,T24 and EJ) was detected by real-time quantitative polymerase chain reaction (qRT-PCR).Two of the least miR-216a-5p-expressed cell lines 5637 and J82 were selected as the experimental object.The experiment was divided into two groups:the control group (transfected with miR-NC) and the experimental group (transfected with miR-216a-5p).The expression of PAK2 mRNA was detected by qRT-PCR.The expression of PAK2,p-Akt and p-ERK protein was detected by Western blot.Cell counting kit-8 (CCK-8) and clone formation assay were used to detect the vitality and proliferation of bladder cancer cells.Flow cytometry was used to detect apoptosis.Results The expression levels of miR-216a-5p in bladder cancer cell lines were lower than normal bladder cells.The expression of PAK2 mRNA and protein was significantly decreased in the experimental group.The expression of PAK2 mRNA in the control and experimental groups were 1.01 ±0.15 and 0.40 ±0.11 (P ＜0.01) in 5637 cells.The expression of PAK2 mRNA in the control and experimental groups were 1.00 ± 0.09 和 0.56 ± 0.14(P ＜ 0.01) in J82 cells.The expression of p-Akt and p-ERK protein was significantly decreased.The cell viability of the experimental group was significantly inhibited,and the proliferative ability was significantly decreased.The apoptosis of the experimental group was significantly increased (P ＜ 0.01).Conclusion miR-216a-5p is low-expressed in a variety of bladder cancer cell lines.It can inhibit PAK2 gene expression in vitro,inhibit the proliferation of bladder cancer cell lines 5637 and J82,promote cell apoptosis,and may become a target molecule with biotherapeutic significance.