Aims: SIRT1 is an NAD+-dependent deacetylase implicated in beneficial metabolic effects and longevity. We have examined how SIRT1 controls hepatic lipid metabolism by deacetylating and altering the activities of two important metabolic regulators, a key lipogenic activator SREBP-1c and the bile acid receptor and negative regulator of lipogenesis, FXR. We also examined how hepatic SIRT1 is negatively regulated by elevated microRNA-34a (miR- 34a) in obesity and further examined the miR-34a/SIRT1 regulatory axis as a potential therapeutic target. Methods: Proteomic, biochemical, and functional studies were utilized to examine the effects of SIRT1-regulated acetylation of SREBP-1c and FXR on liver metabolism. Downregulation and overexpression of miR-34a were utilized to test if miR-34a directly targets both SIRT1 and Nampt1, a critical enzyme increasing cellular NAD+ levels. Anti-miR- 34a experiments were performed in dietary obese mice. Results: Acetylation of SREBP-1c at Lys-289/309, regulated by p300 acetylase and SIRT1 deacetylase, increased its lipogenic activity by enhancing protein stability and binding to lipogenic genes. In contrast, FXR acetylation at Lys-217 decreased transactivation activity by inhibiting its heterodimerization with RXRα and DNA binding. Remarkably, acetylation levels of SREBP-1c and FXR were highly elevated in obese mice, which have markedly decreased SIRT1 levels and abnormally elevated miR-34a levels. Further studies suggested that miR-34a targets SIRT1 and Nampt1 by directly binding to the 3'UTR of their mRNAs, and downregulation of the elevated miR-34a in obesity restored SIRT1, Nampt1, and NAD+ levels with decreased lipogenesis, increased insulin and glucose tolerance, improved ER stress, and decreased inflammation. Conclusion: These results suggest that SIRT1 suppresses hepatic lipogenesis by inhibiting SREBP-1c and activating FXR via protein deacetylation. Reducing acetylation of these proteins by targeting SIRT1 may be useful for treating metabolic disorders. Furthermore, targeting the aberrantly regulated miR-34a/SIRT1-Nampt1 axis with anti-miR-34a may have potential for treating metabolic disorders.