The metabolic improvement effects of Lactobacillus casei IOB-P9 oat postbiotics on high-fat diet-induced obese rats were investigated through 6 consecutive weeks of gavage intervention, followed by measurements of body weight, serum biochemical indices, and liver histopathological changes. The results demonstrated that IOB-P9 oat postbiotics led to a significant increase in high-density lipoprotein cholesterol (HDL-C, 20.98%~55.94%), while total cholesterol (TC, 14.40%~30.48%), triglycerides (TG, 53.86%~71.77%), low-density lipoprotein cholesterol (LDL-C, 31.92%~46.92%), and fasting glucose (Glu, 42.22%~70.94%) were significantly reduced (P<0.05). Additionally, serum leptin (LEP) and corticosterone (CORT) levels were decreased by 40.10%~57.93% and 20.90%~40.16%, respectively (P<0.05). In terms of liver function, the activities of alanine aminotransferase (ALT) and aspartate aminotransferase (AST) were reduced by 59.65%~74.88% and 37.31%~59.88%, respectively, whereas the alkaline phosphatase (ALP) activity was significantly improved. Histopathological analysis of liver tissues revealed that hepatic steatosis was alleviated, and cell arrangement was restored to near-normal in the intervention group. In conclusion, IOB-P9 oat postbiotics significantly ameliorated obesity-related metabolic disorders by regulating lipid metabolism, improving hormonal balance, and repairing liver damage, thereby providing a theoretical foundation for the development of functional food.