Non-alcoholic fatty liver disease (NAFLD) is currently the most common type of chronic liver disease. Semaglutide is a glucose-lowering drug administered for the treatment of type 2 diabetes mellitus (T2DM) and is clinically effective in the treatment of NAFLD. X-box binding protein 1 (XBP1) is related to the pathogenesis of both NAFLD and T2DM. The aim of the present study was to demonstrate whether the underlying mechanism of semaglutide treatment for NAFLD is via downregulation of the inositol-requiring transmembrane kinase/endonuclease-1α (IRE1α)-XBP1-CCAAT/enhancer binding protein α (C/EBPα) signaling pathway in macrophages.In the present study, NAFLD cell modeling was induced by oleic acid (0.4 m<sc>m</sc>) and palmitic acid (0.2 m<sc>m</sc>). Hepatocytes (AML12) and macrophages (RAW264.7) were co-cultured in 6-well Transwell plates. Semaglutide (60 or 140 n<sc>m</sc>) was administrated for 24 h, while pioglitazone (2 μ<sc>m</sc>) and toyocamycin (200 n<sc>m</sc>) were used as a positive control drug and a XBP1 inhibitor, respectively. Autophagy and apoptosis of AML12 cells were detected by transmission electron microscopy and Western blotting (WB). Hepatocyte steatosis was evaluated by adopting total intracellular triglyceride determination, analysis of the relative expression of proteins and genes associated with lipid metabolism and hepatocyte Oil red O staining. Detection of inflammation factors was conducted by ELISA and WB. To explore the underlying mechanism of NAFLD treatment with semaglutide, the relative expression of related proteins and genes were tested.Our study demonstrated that semaglutide treatment improved autophagy and inhibited apoptosis of hepatocytes, while notably ameliorating steatosis of hepatocytes. In addition, inflammation was attenuated in the NAFLD cell co-culture model after semaglutide administration. Semaglutide also significantly reduced the protein and gene expression levels of the IRE1α-XBP1-C/EBPα signaling pathway in macrophages.Semaglutide partially ameliorated NAFLD by downregulating the IRE1α-XBP1-C/EBPα signaling pathway in macrophages. These findings may provide a potential theoretical basis for semaglutide therapy for NAFLD.© 2024 S. Karger AG, Basel.