Erectile dysfunction (ED) is a common diabetic complication. Recent evidence has illuminated the role of hydrogen sulfide (H₂S) as a dynamic mediator of the erection process. H₂S is a potent endogenous relaxant gas. It has been shown to relax human and animal penile tissue in vitro and induce erection in animals in vivo. The reported penile expression of H₂S-synthesizing enzymes also supports the potential role of the endogenous L-cysteine/H₂S pathway in penile homeostasis. Several pathological changes take place in the diabetic penile tissue, including inflammation, oxidative stress, neuropathy and fibrosis of the corpus cavernosum (CC), the major erectile structure of the penis. The present study is experimental and has been performed in the diabetic rat model. The study will investigate the role of H₂S as a potential protective mediator against diabetes-induced structural and functional alterations in the CC by examining if it: (1) reduces corporal contraction and/or enhances corporal relaxation following pharmacological stimulation, (2) attenuates fibromuscular changes in diabetic CC, and (3) whether there is a link with H₂S plasma/urine level and CC tissue generation, as well as studying the expression of some proteins in the transforming growth factor (TGF)-β1-associated pathway. The major findings of the study reveal that- compared to the nondiabetic controls - the diabetic animals CC showed: (1) augmented contraction and attenuated relaxation in response to phenylephrine and carbachol, respectively, (2) marked fibromuscular degeneration with a significantly lower smooth muscle/collagen ratio and upregulation of TGF-β-1/Smad/CTGF fibrosis signaling pathway, (3) reduced H₂S plasma and urinary levels and cavernosal tissue generation. Chronic GYY4137 treatment prevented most of these pathological changes in diabetic CC, thus may be considered a potential new strategy for the prevention and/or treatment of diabetes-induced ED.