Aim: To determine the efficacy of human relaxin-2 (hRLX2) in reversing radiation-induced bladder fibrosis and lower urinary tract dysfunction (LUTD). Radiation cystitis is a consequence of radiotherapy for pelvic malignancies. Acutely, irradiation leads to reactive oxygen/nitrogen species in urothelial cells, apoptosis, barrier disruption, and inflammation. Chronically, this results in collagen deposition, bladder fibrosis, and attenuated storage and voiding functions. In severe cases, cystectomies are performed as current therapies do not reverse fibrosis. Methods: We developed a mouse model for selective bladder irradiation (10 Gray; 1 Gy=100 rads) resulting in chronic fibrosis within 6 weeks, with decreased bladder compliance, contractility, and overflow incontinence. Seven weeks post-irradiation, female C57Bl/6 mice were continuously infused with hRLX2 (400μg/kg/day/14 days) or vehicle (saline) via subcutaneous osmotic pumps. Mice were evaluated in vivo using urine spot analysis, cystometrograms and external urethral sphincter electromyograms; and in vitro using length-tension measurements, Western blots, histology, and immunohistochemistry. Results: hRLX2 reversed fibrosis, decreased collagen content, improved bladder wall architecture, and increased bladder compliance, detrusor smooth muscle Cav1.2 expression and detrusor contractility in mice with chronic radiation cystitis. hRLX2 treatment outcomes were likely caused by the activation of RXFP1/2 receptors which are expressed on the detrusor. Conclusion: hRLX2 may be a new therapeutic option for rescuing bladders with chronic radiation cystitis.