The pathophysiology behind radiation cystitis is poorly understood. Here we investigated whether bladder irradiation affects the immune system of the rat urinary bladder. Female rats were sedated and exposed to one single radiation dose of 20 Gy or only sedated (controls) and killed 16 h to 14 days later. Rats were placed in a metabolic cage at 16 h, 3 days, 7 days and 14 days following bladder irradiation. The urinary bladders were harvested and analysed with qPCR, immunohistochemistry and/or Western blot for the expression of interferon (IFN)‐γ, interleukin (IL)‐1β, IL‐2, IL‐4, IL‐5, IL‐6, IL‐10, IL‐13, nitric oxide synthases (eNOS, iNOS and nNOS), tumour necrosis factor (TNF)‐α and toll‐like receptor 4 (TLR4). Urine was collected and analysed for IL‐6 and nitrite (reflecting nitric oxide activity) with ELISA and the Griess reaction, respectively. Irradiation increased bladder frequency and decreased voiding volumes 14 days following bladder irradiation. Bladder irradiation increased the expression of IL‐10 and collagen in the bladder, while TLR4 and IL‐6 expressions were decreased in the urothelium concomitantly with a decrease in mast cells in the submucosa and urine levels of IL‐6 and nitrite. The present findings show that bladder irradiation leads to urodynamic changes in the bladder and may suppress important immunoregulatory pathways in the urinary bladder.