Aims: H₂S, a third member of gasotransmitter family along with nitric oxide and carbon monoxide, exerts a wide range of cellular and molecular actions in our body. Cystathionine gamma-lyase (CSE) is a major H₂S-generating enzyme in our body. Aging at the cellular level, known as cellular senescence, can result from increases in oxidative stress. The aim of this study was to investigate how H₂S attenuates oxidative stress and delays cellular senescence. Results: Here we showed that mouse embryonic fibroblasts isolated from CSE knockout mice (CSE KO-MEFs) display increased oxidative stress and accelerated cellular senescence in comparison with MEFs from wild-type mice (WT-MEFs). The protein expression of p53 and p21 was significantly increased in KO-MEFs, and knockdown of p53 or p21 reversed CSE deficiency-induced senescence. Incubation of the cells with NaHS (a H₂S donor) significantly increased the glutathione (GSH) level and rescued KO-MEFs from senescence. Nrf2 is a master regulator of the antioxidant response, and Keap1 acts as a negative regulator of Nrf2. NaHS S-sulfhydrated Keap1 at cysteine-151, induced Nrf2 dissociation from Keap1, enhanced Nrf2 nuclear translocation, and stimulated mRNA expression of Nrf2-targeted downstream genes, such as glutamate–cysteine ligase and GSH reductase. Innovation: These results provide a mechanistic insight into how H₂S signaling mediates cellular senescence induced by oxidative stress. Conclusion: H₂S protects against cellular aging via S-sulfhydration of Keap1 and Nrf2 activation in association with oxidative stress. Antioxid. Redox Signal. 18, 1906–1919.