BACKGROUND: There's a scarcity of drugs effective against nonalcoholic steatohepatitis (NASH). Exosomes from Human umbilical cord mesenchymal stem cells (huc-MSCs) show potential in managing glycolipid metabolism and the immune response. Therefore, further investigations are required to explore their application in NASH and the underlying mechanisms. METHODS: C57BL/6J mice were fed with a western diet for 12 weeks to induce NASH, and huc-MSCs exosomes (MSCs-exo) were administered during the feeding period. The effect of MSCs-exo was evaluated by monitoring changes in body weight, fat distribution, blood glucose, and insulin levels, and analyzing pathological alterations in liver tissue. Mechanism investigations were carried out using flow cytometry, immunofluorescence staining, and other experimental techniques. RESULTS: MSCs-exo could reduce liver fat, inflammation, fibrosis, and improved metabolism to alleviate the progression of NASH. Besides, MSCs-exo could decrease macrophage accumulation in the liver, encouraging M2 over M1 macrophage polarization. Furthermore, our study found that MSCs-exo had a high expression of miR-24-3p, which may regulate macrophage polarization by targeting the interferon-stimulated genes (STING) gene in macrophages, with its overexpression amplifying MSCs-exo's NASH benefits. CONCLUSIONS: These findings suggest that the therapeutic effect of MSCs-exo on NASH may be attributed to the regulation of macrophage M2 polarization through miR-24-3p targeting STING. This provides a scientific basis for future clinical application.