Bladder cancer is one of the most frequently diagnosed cancers in men. While cystectomy remains the primary treatment, advances in radiotherapy and chemotherapy have highlighted the value of bladder-preserving strategies, which can also enhance patients’ quality of life. Despise these advances, around 20% of patients may still require salvage cystectomy due to tumor radioresistance. This underscores the need to develop radiosensitivity predictive assays. Radiotherapy acts by inducing DNA damage, primarily through DNA double-strand breaks, which can significantly affect treatment outcomes if left unrepaired. In addition to activating DNA repair pathways, the response to radiation also involves the tumor microenvironment, cell death pathways, immune responses and different types of cell death and proliferation receptors. In recent years, personalized medicine, which tailors treatments to individual patients, has gained increasing attention in cancer care. The development of chemo- and radiosensitivity predictive assays has become a key focus of cancer research. Despite the potential impact of such assays on bladder cancer treatment, there is still no reliable test that can help clinicians and informs patients in choosing the best treatment. This review aims to highlight studies that attempted to characterize bladder cancer radiosensitivity and to discuss the potential biomarkers that could be used to develop bladder cancer radiosensitivity predictive assays.