Abstract Body (Do not enter title and authors here): Background Metabolic dysfunction-associated steatotic liver disease (MASLD) is increasing globally due to rising obesity and metabolic syndrome. MASLD can progress to MASH, cirrhosis, and liver cancer, and shares causes with cardiovascular disease. Recent studies have demonstrated that ketone bodies have diverse protective effects, including roles in energy metabolism, antioxidant function, and signal transduction. However, it remains unclear whether ketone bodies have a protective role in fatty liver disease. Aim To clarify the role of ketogenesis in MASLD and examine the therapeutic effect and mechanism of Pemafibrate (PEMA).Method/Result Wild-type mice were fed normal diet (ND) and Gubra Amylin NASH (GAN) diet with water containing Nω-Nitro-L-arginine Methyl Ester Hydrochloride (L-NAME)[MASLD] for 10 weeks. MASLD groups showed significantly elevated body weight and systolic blood pressure compared to ND group. The liver in MASLD showed increased weight and a more yellowish-brown color. Hepatocyte-specific Hmgcs2 deficient mice (Alb-cre;Hmgcs2^flox/flox; Hmgcs2^ΔHEP) and control mice (Hmgcs2^flox/flox; Ctrl) were fed ND or MASLD, accessing the effectiveness of PEMA and the impacts of ketogenesis on MASLD. Liver tissues were stained with HE and Sirius red. Hmgcs2^ΔHEP showed more fatty deposits in the liver compared to Ctrl. Serum samples were collected for biochemical tests. PEMA administration showed no notable improvement in hepatobiliary enzymes and triglycerides (TG). Furthermore, RNA-seq analysis revealed that PEMA-treated Ctrl significantly increased expression of genes involved in fatty acid metabolism and oxidative phosphorylation, such as Aldh2, ACAA2 and Sdha. These results indicated that PEMA might have therapeutic effects on MASLD, mediating ketogenesis. In vitro experiments, using primary hepatocytes of mice, Real-time PCR analysis indicated the results similar to RNA-seq in vivo, with upregulation of gene expression related to fatty acid metabolism and oxidative phosphorylation. Conclusion Ketone body metabolism plays a crucial role in the progression of MASLD, and its impairment may lead to worsening hepatic steatosis. Moreover, the beneficial effects of PEMA on fatty liver appear to require intact ketone metabolism, suggesting that individual differences in therapeutic response may be influenced by metabolic status. These findings highlight the potential of ketone body metabolism as a novel therapeutic target for MASLD.