Keloid is a common dermatofibrotic disease with excessive skin fibroblast proliferation. Hydrogen sulfide (H2S) as the third gasotransmitter improves fibrosis of various organs and tissues. Our study is aimed at investigating the effects and possible mechanisms of H2S on skin fibroblast proliferation. Scar tissues from six patients with keloid and discarded skin tissue from six normal control patients were collected after surgery, respectively. Plasma H2S content and skin H2S production in patients with keloid were measured. Keloid fibroblasts and transforming growth factor-β1- (TGF-β1, 10 ng/mL) stimulated normal skin fibroblasts were pretreated with H2S donor as NaHS (50 μM) for 4 h. Cell migration after scratch was assessed. The expressions of α-smooth muscle actin (α-SMA), proliferating cell nuclear antigen (PCNA), collagen I, and collagen III were detected by immunofluorescence, real-time PCR, and/or Western blot. Intracellular superoxide anion and mitochondrial superoxide were evaluated by dihydroethidium (DHE) and MitoSOX staining, respectively. Mitochondrial membrane potential was detected by JC-1 staining. Apoptotic cells were detected by TDT-mediated dUTP nick end labeling (TUNEL). The expressions of receptor interacting protein kinase 1 (RIPK1), RIPK3, and mixed lineage kinase domain-like protein (MLKL) were measured by Western blot. We found that H2S production was impaired in both the plasma and skin of patients with keloid. In keloid fibroblasts and TGF-β1-stimulated normal skin fibroblasts, exogenous H2S supplementation suppressed the expressions of α-SMA, PCNA, collagen I, and collagen III, reduced intracellular superoxide anion and mitochondrial superoxide, improved the mitochondrial membrane potential, decreased the positive rate of TUNEL staining, and inhibited RIPK1 and RIPK3 expression as well as MLKL phosphorylation. Overall, H2S suppressed skin fibroblast proliferation via oxidative stress alleviation and necroptosis inhibition.