Abstract: Objective:To investigate the therapeutic effect of microvesicles (MVs) derived from human umbilical cord mesenchymal stem cells (hUC-MSCs) on rheumatoid arthritis (RA). Methods:In this experiment, microvesicles of human umbilical cord mesenchymal stem cells (hUC-MSCs-MVs) were isolated and constructed to establish the bovine type II collagen induced rheumatoid arthritis (CIA) with DBA/1J mice, which MVs were injected into tail vein of mice, and controls were inject the same volume of PBS. Four weeks later, HE staining was used to assess arthritis index and synovial pathological changes, and the expression of inflammatory factors was detected by ELISA. Bone marrow bone marrow derived macrophage (BMDM) were isolated and treated with LPS for 24 h to induce into pro-inflammatory macrophages. After 24 h of treatment with MVs, the cell supernatant was collected to detect the expression of inflammatory factors by ELISA, and the expression of surface markers CD80 and CD86 of pro-inflammatory macrophages was measure by flow cytometer. Results:The results suggested that the arthritis score of the MVs group was decreased (P＜0.05). After MVs treatment in vivo, the expression of inflammatory factors (IL-1β, IL-6 and TNF-α) were down-regulated (P＜0.01). HE staining showed that the inflammation of ankle joint was alleviated. The results demonstrated that hUC-MSCs-MVs effectively reduced the expression of inflammatory factors and the expression levels of CD80 and CD86 in macrophage stimulated by LPS (P＜0.05). Conclusions:hUC-MSCs-MVs can effectively relieve the symptoms of rheumatoid arthritis in CIA mice.