A healthy vascular endothelium plays an essential role in modulating vascular tone by producing and releasing vasoactive factors such as nitric oxide (NO). Endothelial dysfunction (ED), the loss of the endothelium physiological functions, results in the inability to properly regulate vascular tone, leading to hypertension and other cardiovascular risk factors. Alongside NO, the gasotransmitter hydrogen sulfide (H2S) has emerged as a key molecule with vasodilatory and antioxidant activities. Since a reduction in H2S bioavailability is related to ED pathogenesis, natural H2S donors are very attractive. In particular, we focused on the sulfur-containing amino acid S-allyl cysteine (SAC), a bioactive metabolite, of which black garlic is particularly rich, with antioxidant activity and, among others, anti-diabetic and anti-hypertensive properties. In this study, we analyzed the protective effect of SAC against ED by evaluating reactive oxygen species level, H2S release, eNOS phosphorylation, and NO production (by fluorescence imaging and western blot analysis) in Bovine Aortic Endothelial cells (BAE-1). Furthermore, we chemically characterized a Black Garlic Extract (BGE) for its content in SAC and other sulfur-containing amino acids. BGE was used to carry out an analysis on H2S release on BAE-1 cells. Our results show that both SAC and BGE significantly increase H2S release. Moreover, SAC reduces ROS production and enhances eNOS phosphorylation and the consequent NO release in our cellular model. In this scenario, a natural extract enriched in SAC could represent a novel therapeutic approach to prevent the onset of ED-related diseases.