Objective To investigate the effects of urothelial carcinoma antigen 1 long non-coding RNA(LncRNA UCA1) on the proliferation, apoptosis, and radiosensitivity of bladder cancer cells by regulating miR-520a-5p. Methods LncRNA UCA1 and miR-520a-5p were detected in normal bladder epithelial (HCV-29) and human bladder cancer (SW780, HT1376, BIU87 and T24) cell lines by quantitative reverse transcription-polymerase chain reaction. T24 cells were treated with different radiation doses (0~8 Gy) and cell proliferation activity was detected.T24 cells were assigned to Control, sh-NC, sh-UCA1, sh-UCA1 + anti-miR-NC, and sh-UCA1 + anti-miR-520a-5p groups. Cells in each group were treated with a radiation dose of 2 Gy, and cell proliferation, apoptosis, and cyclin D1, Ki-67, Bax, and Caspase-3 protein expression levels were detected. The targeting relationship between LncRNA UCA1 and miR-520a-5p was verified by dual-luciferase reporter gene, fluorescence in situ hybridization, and RNA immunoprecipitation assays. A nude mouse tumor xenotransplantation model was established, and the effect of LncRNA UCA1 on the radiosensitivity of bladder cancer was verified. Results LncRNA UCA1 was increased and miR-520a-5p was decreased in bladder cancer cell lines. Treating T24 cells with different radiation doses (0~8 Gy) reduced cell proliferation activity in the sh-UCA1 group compared with the sh-NC group, in line with increasing radiation dose (P<0. 05). T24 cells and a radiation dose of 2 Gy were therefore selected for subsequent experiments. Knockdown of LncRNA UCA1 in T24 cells inhibited cell proliferation, promoted cell apoptosis, increased radiosensitivity, down-regulated cyclin D1 and Ki-67, and upregulated Bax and Caspase-3 (P<0. 05). miR-520a-5p antagonist weakened the impacts of LncRNA UCA1 knockdown on the proliferation, apoptosis, and radiosensitivity of bladder cancer cells (P<0. 05). LncRNA UCA1 targeted the negative regulation of miR-520a-5p. Knockdown of LncRNA UCA1 combined with radiotherapy inhibited the growth of bladder cancer tumor transplants and increased their radiosensitivity (P<0. 05). Conclusions LncRNA UCA1 is up-regulated in bladder cancer cells. Knockdown of LncRNA UCA1 can inhibit cell proliferation, induce apoptosis, and enhance the radiosensitivity of bladder cancer cells by up-regulating miR-520a-5p.