AIM: The goal of this study was to determine the role of histone deacetylase 9 (HDAC9) in the development of diet-induced metabolic dysfunction-associated steatohepatitis (MASH) and white adipose tissue (WAT) dysfunctions. METHODS: We fed male and female mice with global Hdac9 knockout (KO) and their wild-type (WT) littermates an obesogenic high-fat/high-sucrose/high-cholesterol (35%/34%/2%, w/w) diet for 20 weeks. RESULTS: Hdac9 deletion markedly inhibited body weight gain and liver steatosis with lower liver weight and triglyceride content than WT in male mice but not females. Consistently, hepatic expression of genes crucial for de novo lipogenesis was markedly suppressed only in male, but not female, Hdac9 KO mice. However, Hdac9 deletion had a minimal effect on hepatic inflammation and fibrosis. In WAT, Hdac9 KO showed less adipocyte hypertrophy, inflammation, and fibrosis in male mice compared with WT. In addition, indirect calorimetry demonstrated that male Hdac9 KO mice had significantly higher metabolic rates, respiratory exchange ratios, and energy expenditure without altering physical activities than WT, which was not observed in female mice. CONCLUSIONS: Our findings indicate that global deletion of Hdac9 prevented the development of obesity, hepatic steatosis, and WAT inflammation and fibrosis in male mice with diet-induced obesity and MASH, suggesting that a sex-dependent role of HDAC9 may exist in the pathways mentioned above.