Objective  To investigate the  the effect of exosomes derived from bone marrow mesenchymal stem cells (BMSCs) on the polarization of liver Kupffer cells.     Methods  After BMSCs were isolated and cultured in vitro, their surface molecular expression was identified by flow cytometry, and their differentiation potential was induced and identified by osteogenic and lipogenic induction media. Exosomes were extracted from the supernatant of BMSCs culture by exosomes extraction kit, and their morphology was observed by electron microscopy, and surface molecular expression was identified by flow cytometry. In vitro cultured Kupffer cells were randomly divided into normal culture, lipopolysaccharide(LPS) stimulation and LPS co-culture groups, and morphological changes in Kupffer cells were observed under light microscope.Sixty mice were injected intraperitoneally with CCl4 to replicate acute liver injury model and randomized into PBS control and exosomes treatment groups, and the liver histopathology and the expression of liver functional alanine transferase(ALT) and aspartate aminotransferase(AST) were detected by HE staining. Western blotting was used to detect the  expressions of inducible nitric oxide synthase(iNOS) and arginase-1(ARG1) in the three groups of Kupffer cells cultured in vitro and the two groups of liver tissues in vivo. The expression of iNOS, ARG1, interleukin(IL)-1β, tumor necrosis factor(TNF)-α and C-X-C motif chemokine(CXCL)-10 were detected by Real-time PCR.    Results  BMSCs were successfully isolated and had the ability of differentiation of osteoblasts and adipocytes, and expressed CD105 and CD45. The exosomes were bubble-like and expressed CD63 and CD81. Light microscopy showed that exosomes of BMSCs attenuated Kupffer cells activation, and exosomes of BMSCs attenuated pathological changes of liver tissue after injection (P<0.05), decreased the high expression of ALT and AST in liver function (P<0.05); Western blotting showed that ARG1 expression increased in LPS and exosomes co-cultured in vitro and exosomes treated in vivo (P<0.05), iNOS decreased (P<0.05); Real-time PCR showed decreased expression of iNOS, IL-1β, TNF-α and CXCL-10 in LPS and exosomes co-cultured group and exosomes treated group (P<0.05), ARG1 expression increased (P<0.05).    Conclusion  Exosomes derived from BMSCs inhibited M1 type polarization of mouse Kupffer cells.