〔Abstract〕 Objective To investigate the effect of exosomes secreted by human mesenchymal stem cells(hMSCs) on the proliferation and secretion of monocytes. Methods hMSCs were cultured by centrifugation method, and the supernatant of hMSCs was collected. Exosomes were extracted by kit and observed by SEM. CD63 and CD81 levels were tested by Western blot.Monocytes were isolated by density gradient centrifugation. Lipopolysaccharide(LPS) was used as a stimulant to induce proliferation and the synthesis of inflammatory cytokines. After treated by exosomes, MTT viability assay and apoptosis analysis by flow cytometry(FCM) were used to study the proliferative ability. Tumor necrosis factor-α(TNF-α),interleukin-1β(IL-1β),interleukin-6(IL-6) and interleukin-8(IL-8) in the culture supernatant were measured by enzyme-linked immunosorbent assay(ELISA). Results Exosomes secreted by hMSCs were small ball-shaped under SEM. CD63 and CD81 were positively expressed by Western blot. MTT showed that LPS could promote the proliferation of monocytes, while exosomes inhibited the proliferation of monocytes. However, after treated by exosomes, the apoptosis of monocytes significantly increased. ELISA showed that exosomes could inhibit the secretion of TNF-α, IL-1β, IL-6 and IL-8 by monocytes. Conclusion Exosomes secreted by hMSCs can inhibit the proliferation of monocytes and the secretion of TNF-α, IL-1β, IL-6 and IL-8 by monocytes while promote the apoptosis. It is preliminarily proved that hMSC-derived exosomes have immune-regulatory function.