To evaluate the therapeutic potential of human umbilical cord blood mesenchymal stem cells (hUCBMSCs) on promoting erectile function in a rat model of bilateral cavernous nerve (CN) crush injury. Fifty male Sprague-Dawley rats were randomly assigned to sham + PBS group (n = 10), BCNI (bilateral cavernous nerve crush injury) + PBS group (n = 10), BCNI + hUCBMSCs group (n = 30). At day 28 (n = 10) post-surgery, erectile function was examined and histological specimens were harvested. Compared with BCNI + PBS group, hUCBMSC intracavernous injection treatment significantly increased the mean ratio of ICP/MAP, nNOS-positive nerve fibers in the dorsal penile nerve, smooth muscle content, and smooth muscle to collagen ratio in the corpus cavernousum. Electron microscopy revealed few CN and major pelvic ganglion (MPG) lesions in the BCNI + hUCBMSCs group. Injected hUCBMSCs were localized to the sinusoid endothelium of the penis and MPG on day 1, 3, 7, and 28 post-intracavernous injection. hUCBMSCs intracavernous injection treatment improves erectile function by inhibiting corpus cavernosum fibrosis and exerting neuroregenerative effects on cell bodies of injured nerves at MPG in a BCNI rat model.