Nitric oxide (NO) is a multifunctional regulator that is implicated in various physiological and pathological processes. Here we report that administration of NO donor S-nitroso-N-acetylpenicillamine (SNAP) inhibited transforming growth factor-β1 (TGF-β1)-induced epithelial-to-mesenchymal transition (EMT) and apoptosis in mouse hepatocytes. Overexpression of inducible NO synthase (iNOS) by transfection of the iNOS-expressing vector, which increased NO production, also inhibited the TGF-β1-induced EMT and apoptosis in these cells. Treatment of cells with proinflammatory mediators, including tumor necrosis factor (TNF)-α, interleukin (IL)-1β, and interferon (IFN)-γ, which increased the endogenous NO production, produced the same inhibitory effect. Furthermore, exogenous NO donor SNAP treatment caused a decrease in the intracellular adenosine triphosphate (ATP) levels. Consistently, depletion of intracellular ATP by mitochondrial uncoupler carbonyl cyanide p-trifluoromethoxyphenylhydrazone (FCCP) inhibited the TGF-β1-induced EMT and apoptosis, suggesting that an NO-induced decrease of ATP involved in the NO-mediated inhibition of TGF-β1-induced EMT and apoptosis. NO and FCCP also inhibited TGF-β1-induced STAT3 activation, suggesting that signal transducer and activator of transcription 3 inactivation is involved in the NO-induced effects on TGF-β1-induced EMT and apoptosis. Conclusion: Our study indicates that NO plays an important role in the inhibition of TGF-β1-induced EMT and apoptosis in mouse hepatocytes through the downregulation of intracellular ATP levels. The data provide an insight into the in vivo mechanisms on the function of NO during the processes of both EMT and apoptosis. (HEPATOLOGY 2009.)