Abstract: Objective To evaluate the effect and investigate the mechanism of human umbilical cord mesenchymal stem cells（hucMSCs）culture supernatant on M1-type macrophages. Methods The mouse macrophage-like cell line RAW264.7 was used as the macrophage cell line, planted in the 6-well plate and treated when the confluence reached approximately 70%. Conditional DMEM medium（CM）containing 50% hucMSCs culture supernatant was prepared. Macrophages were divided into three groups. In the blank group, the cells were cultured in 2 ml DMEM medium for 24 h and then cultured in 2 ml fresh DMEM medium for 24 h. In the DMEM group, the cells were cultured in 2 ml DMEM medium containing 200 ng/ml LPS for 24 h, followed by 24-h culture in 2 ml fresh DMEM medium. In the CM group, the cells were cultured in 2 ml DMEM medium containing 200 ng/ml LPS for 24 h and subsequently cultured in 2 ml fresh CM medium for 24 h. The culture medium and macrophages from each group were gathered for subsequent experiments. Substances having cell membrane components in CM were subject to PKH67 staining（green）and RAW264 with DAPI staining（blue）. The phagocytosis of cell membrane components in hucMSCs-CM by macrophages was observed under fluorescence microscope. The expression levels of pro-inflammatory factor TNF-α and anti-inflammatory factor IL-10 were analyzed by real-time fluorescence quantitative polymerase chain reaction（RT-qPCR）and flow cytometry multi-factor analysis. The phenotype of macrophages was identified by flow cytometry. Results Fluorescence microscopy revealed that RAW264.7 phagocytosis substances containing cell membrane components in the CM group were increased with time in the hucMSCs supernanant. In macrophage polarization experiment, RT-qPCR indicated that the expression level of anti-inflammatory factor interleukin-10（IL-10）mRNA in the CM group was significantly lower than that in the DMEM group, and the expression level of tumor necrosis factor-α（TNF-α）mRNA, a proinflammatory mediator, was significantly lower compared with those in the blank and DMEM groups（all P<0.05）. Flow cytometry multi-factor analysis showed that the expression level of anti-inflammatory factor IL-10 in the CM group was remarkably lower than that in the DMEM group, and the expression level of pro-inflammatory factor TNF-α mRNA was significantly lower than those in the blank and DMEM groups（all P<0.05）. Flow cytometry analysis showed that the proportion of F4/80⁺CD206⁺CD86^- type M2 macrophages in the CM group was higher compared with that in the DMEM group. Conclusion Macrophages may induce the polarization of M1-type macrophages into M2-type macrophages by phagocytosis of the membranous components in the hucMSCs culture supernanant, thereby promoting the anti-inflammatory response.