Cyclosporine A (CsA) is used as an immunosuppressive agent, and its prominent side effect is the induction of gingival overgrowth. Snail is a master regulator of epithelial–mesenchymal transition (EMT). EMT under pathological processes could lead to fibrotic changes. The purpose of this study was to investigate the role of Snail in the pathogenesis of CsA-induced gingival overgrowth. Methods: The effect of CsA on normal human gingival fibroblasts (HGFs) was used to elucidate whether Snail expression could be induced by CsA by using quantitative real-time reverse transcription–polymerase chain reaction and western blot. The cell proliferation rate in CsA-treated HGFs with Snail lentiviral-mediated short hairpin RNA interference (shRNAi) knockdown was evaluated by tetrazolium bromide reduction assay. Results: CsA increased the Snail transcript and Snail protein expression in HGFs in a dose-dependent manner (p < 0.05). In addition, downregulation of Snail by lentiviral infection significantly reduced CsA-stimulated cell proliferation in HGFs (p < 0.05). Conclusion: CsA stimulated Snail expression and cell proliferation in HGFs, while silencing Snail could effectively reverse these phenomena. These results may provide new avenues for the design of novel antifibrotic therapies for CsA-induced gingival overgrowth through targeting Snail.