A Western-style high-fat diet is known to cause vascular dysfunction and oxidative stress. H2S contributes to the regulation of vascular function and acts as a vasoprotective molecule; however, the effects of high-fat diet on vascular H2S production and function are not known. The aim of this study was to investigate the effects of high-fat diet on vascular function and H2S production. Wistar hooded rats were fed a western diet (WD, 21 % fat) or control rat chow (6 % fat) for 12 weeks. At the end of the experiment, the aorta was collected for assessing vascular function and NO and H2S bioavailability. Superoxide anion production was quantitated by lucigenin-enhanced chemiluminescence. The expression of NADPH oxidase subunit Nox2 and the H2S-producing protein cystathionine-γ-lyase (CSE) were examined by Western blotting. WD rats had significantly higher body weight and body fat than control (p < 0.001). Endothelial function and NO bioavailability were significantly reduced in the WD group (p < 0.05), but vascular smooth muscle cell function was unaffected. Vascular superoxide production and Nox2 expression were significantly increased in the aorta from WD rats. L-Cysteine-induced vasorelaxation was reduced in the WD group (p < 0.05) and insensitive to the inhibition of the CSE. In addition, vascular H2S bioavailability and CSE expression were significantly reduced in the aorta from WD rats (p < 0.01). These data show that fat feeding induces vascular oxidative stress and a reduction in endothelial function. Furthermore, there is a reduced capacity for both basal and stimulated vascular H2S production via CSE in fat fed rats.