Objective To investigate the regulation of IL-1β on the expression of CD200 in human umbilical cord mesenchymal stem cells (hUC-MSCs), its role in macrophage polarization and the underlying mechanism. Methods hUC-MSCs were isolated and cultured in serum-free medium. Morphological observation and the expressions of CD73, CD90, CD105, CD14, CD34, CD45 and HLA-DR were detected by flow cytometry to confirm the properties of mesenchymal stem cells. hUC-MSCs were treated with IL-1β at the final concentration of 20 ng/mL for 24 hours. The proportion of CD200 positive cells was measured by flow cytometry. Real-time quantitative PCR and Western blot analysis were used to detect CD200 mRNA and protein expression levels. hUC-MSCs infected with CD200 overexpression (OE-CD200) and its negative control (OE-NC) lectin virus were treated with IL-1β and co-cultured with PMA-activated THP-1 macrophages. The proportion of CD11c and CD206 positive cells was measured by flow cytometry. hUC-MSCs were treated with IL-1β in combination with PD98059, and the expression of MAPK signaling pathway-related proteins and its effect on CD200 expression were detected by Western blot analysis. Results IL-1β significantly down-regulated the expression of CD200 protein and the proportion of CD200 positive cells. Overexpression of CD200 significantly up-regulated the expression of CD200 in hUC-MSCs, and increased the proportion of CD206-positive macrophages. IL-1β activated the ERK1/2 signaling pathway in hUC-MSCs, and PD98059 up-regulated the expression of CD200 protein in hUC-MSCs treated with IL-1β. Conclusion IL-1β inhibits the expression of CD200 by activating ERK1/2 signaling pathway, and reduces the immunosuppressive effect of hUC-MSCs on regulating the M2-type polarization of macrophages.