Renal fibrosis is a common histomorphological feature of renal aging and chronic kidney diseases of all etiologies, and its initiation and progression are substantially influenced by aberrant epigenetic modifications of fibrosis-susceptible genes, yet without effective therapy. "Epigenetic diets" exhibit tissue-protective and epigenetic-modulating properties; however, their anti-renal fibrosis functions and the underlying mechanisms are less understood. In this study, we show that genistein, a phytoestrogenic isoflavone enriched in dietary soy products, exhibits impressive anti-renal fibrosis activities by recovering epigenetic loss of Klotho, a kidney-enriched anti-aging and fibrosis-suppressing protein. Mouse fibrotic kidneys induced by UUO (unilateral ureteral occlusion) displayed severer Klotho suppression and adverse expression of renal fibrosis-associated proteins, but genistein administration markedly recovered the Klotho loss and attenuated renal fibrosis and the protein expression abnormalities. The examination of possible causes of the Klotho recovery revealed that genistein simultaneously inhibited histone 3 deacetylation of Klotho promoter and normalized the promoter DNA hypermethylation by suppressing elevated DNA methyltransferase DNMT1 and DNMT3a. More importantly, genistein's anti-renal fibrosis effects on the renal fibrotic lesions and the abnormal expressions of fibrosis-associated proteins were abrogated when Klotho is knockdown by RNA interferences in UUO mice. Thus, our results identify Klotho restoration via epigenetic histone acetylation and DNA demethylation as a critical mechanism of genistein's anti-fibrosis function and shed new lights on the potentials of epigenetic diets in preventing or treating aging or renal fibrosis-associated kidney diseases. KEY MESSAGES: Genistein prevents renal fibrosis and the associated Klotho suppression in UUO mice. Genistein upregulates Klotho in part by reversing the promoter histone 3 hypoacetylation. Genistein also preserves Klotho via relieving Klotho promoter hypermethylation. Genistein demethylates Klotho promoter by inhibiting aberrant DNMT1/3a expression. Genistein restoration of Klotho is essential for its anti-renal fibrosis function.