〔Abstract〕 Objective To analyze the expression and clinical significance of circ-RACGAP1 in bladder cancer tissues, and to explore the influence and mechanism of circ-RACGAP1 on the malignant biological behavior of bladder cancer cells. Methods The expression of circ-RACGAP1 in bladder cancer tissues was explored through the TCGA database, and the relationship between the expression of circ-RACGAP1 and the clinicopathological features of bladder cancer patients was analyzed. The expression of circ-RACGAP1 in cell lines 5637, T24, J82, RT-4 and UM-UC-3 was analyzed by quantitative real-time PCR(qPCR). The circ-RACGAP1 knockdown plasmid was transfected into T24 cells by lipofection technology. Colony formation assay, scratch assay and Transwell assay were used to analyze the effects of knocking down circ-RACGAP1 on the proliferation, migration and invasion of T24 cells, respectively. The targeted binding between circ-RACGAP1 and miR-4324 was verified using deepBase, Circbank, CircInteractome, circRNABase databases and a fluorescent reporter system. The effect of knocking down circ-RACGAP1 on the expression of miR-4324 in T24 cells was detected by qPCR. Western blot was used to detect the effect of knocking down circ-RACGAP1 on the expression of recombinant rac-GTPase activating protein 1(RACGAP1) protein and phosphatidylinositol-3-kinase/protein kinase B(PI3K/AKT) signaling pathway proteins in T24 cells. Results circ-RACGAP1 was highly expressed in bladder cancer tissues(P<0.01), and its expression increased with the clinical stage of the patients(P<0.01). The expression of circ-RACGAP1 in bladder cancer cell lines was significantly higher than that in normal human bladder epithelial cells(all P<0.01). Compared with the control group, the proliferation, migration and invasion abilities of T24 cells in the sh-circ-RAC-GAP1 group significantly decreased(allP<0. 01). circ-RACGAP1 could target and inhibit the expression of miR-4324(P<0. 01). Compared with the control group, the expression level of RACGAP1 protein in T24 cells in the sh-circ-RACGAP1 group decreased(P<0. 01), and the expression levels of PI3K/AKT signaling pathway proteins phosphatidylinositol-3-kinase(p-PI3K), phosphorylated protein kinase B(p-AKT), nuclear factor kappa B(NF-κB) decreased(allP<0. 01).Conclusion circ-RACGAP1 is highly expressed in bladder cancer tissues and cell lines, knocking down circ-RACGAP1 can inhibit the malignant biological behavior of T24 cells, and circ-RACGAP1 plays a role by inhibiting the expression of miR-4324 and activating the PI3K/AKT signaling pathway.