Objective: Radiation therapy (RT) is an effective and common treatment for prostate cancer. Although RT-induced erectile dysfunction (ED) is one of the particularly devastating side effects, there is a lack of preclinical studies on RT-induced ED. The aim of this study was to develop a RT-induced ED rat model. Design and Method: 10 adult male Sprague-Dawley (SD) rats were divided into control (n=5) and RT group (n=5). Irradiated rats received external pelvic radiation in a single 24 Gy fraction. After 10 weeks, intracavernous pressure (ICP) and mean arterial pressure (MAP) were measured with cavernous nerve electrical stimulation. Results: ICP/MAP ratios in the RT group were significantly lower than those in the control group (p=0.009). In the RT group, only focal loss of hair on irradiated area was observed, and there were no significant physical and physiological changes. Conclusions: In SD rats, external pelvic radiation in a single 24 Gy fraction induced decreased erectile function significantly, and did not cause serious adverse events. These results suggest that a rat model induced by external pelvic radiation in a single 24 Gy fraction is feasible and safe.