Objective: To discuss the effects of long non-coding ribonucleic acid urothelial carcinoma antigen 1 (LncRNA UCA1) on the proliferation, apoptosis and radiosensitivity of bladder cancer cells by regulating microRNA-520a-5p (miR-520a-5p). Methods: QRT-PCR was used to detect the LncRNA UCA1 and miR-520a-5p in normal bladder epithelial cell line (HCV-29) and human bladder cancer cell line (SW780, HT1376, BIU87 and T24). T24 cells were treated with different radiation doses (0-8 Gy), and cell proliferation activity was detected. T24 cells were assigned into control group, sh-NC group, sh-UCA1 group, sh-UCA1+anti-miR-NC group, and sh-UCA1+anti-miR-520a-5p group. Cells in each group were treated with a radiation dose of 2 Gy, and the cell proliferation, apoptosis, and CyclinD1, Ki-67, Bax, and caspase-3 proteins were detected. The dual luciferase reporter gene assay, fluorescence in situ hybridization (FISH) assay, and RNA immunoprecipitation assay were used to verify the targeting relationship between LncRNA UCA1 and miR-520a-5p. Nude mouse tumor xenotransplantation model was established, and the effect of LncRNA UCA1 on the radiosensitivity of bladder cancer was verified. Results: The LncRNA UCA1 was increased and miR-520a-5p was decreased in bladder cancer cell lines. After treating T24 cells with different radiation doses (0-8 Gy), the cell proliferation activity in the sh-UCA1 group was conspicuously lower than that in the sh-NC group with the increase of radiation dose (P<0.05). Therefore, T24 cells and radiation dose of 2 Gy were selected. In T24 cells, knocking down LncRNA UCA1 could clearly inhibit cell proliferation, promote cell apoptosis, and increase radiosensitivity, downregulate CyclinD1 and Ki-67, and upregulate Bax and caspase-3 (P<0.05). MiR-520a-5p antagonist could weaken the impacts of knocking down LncRNA UCA1 on proliferation, apoptosis and radiosensitivity of bladder cancer cells (P<0.05). LncRNA UCA1 could target negative regulation of miR-520a-5p. Knockdown of LncRNA UCA1 combined with radiotherapy could conspicuously inhibit the growth of transplanted tumor of bladder cancer and increase the radiosensitivity (P<0.05). Conclusion: The LncRNA UCA1 is up-regulated in bladder cancer cells. Knocking down LncRNA UCA1 can inhibit cell proliferation, induce apoptosis, and enhance the radiosensitivity of bladder cancer cells by up-regulating miR-520a-5p.