Objective To investgate the relationship between bronchiolitis in infant and the decrease in -PMSCs and the mechanism of hp-MSCs in the prevention and treatment of bronchiolitis.Methods Volunteers were recruited according to the inclusion and exclusion criteria. Patients with bronchiolitis were diagnosed by a pediatrician. At the same time, infant placenta was collected. Cell growth was detected by trypan blue exclusion. HpMSCs surface markers were detected by flow cytometry. Separation of peripheral blood mononuclear cells from peripheral blood was operated by density gradient centrifugation with HypaqueFicoll. CD4+T lymphocytes were further isolated by MACS from mononuclear cells. I-9, IL-17, IL-10 and TGF beta1 levels were detected using ELISA method. IL-9, IL-17, IL-10 and TGF beta1 levels were detected using ELISA method. the expression of the gene and protein in Foxp3 and RORγ were respectively measured by wetern blot and Real time PCR. Results It is significant different between two group in the specific dermatitis. The hp-MSCs level in control was significant higher than that in case group. The expression of CD44 and CD29 Lymphocyte, placental hpMSC surface marker in the control group were significantly higher than that in case group. IL17 and IL-9 from CD4+ T lymphocytes were increased by RSV() infection, Compared with that of the control group. The increase in IL-17 and IL-9 level caused by RSV infection was reduced with hpMSCs intervention. Compared with the control group, the levels of CD4+T lymphocytes secreting IL-10 and TGF,1 were significantly reduced in RSV group, and IL10 and TGF,1 level were significantly enhanced in hp-MSCs group. Compared with the control group, the expression of Foxp3 gene and protein were downregulated by RSV infection, the expression of Foxp3 gene and protein were upregulated by hp-MSCs intervention. Compared with the control group, the expression of RORγt gene and protein were upregulated by RSV infection, the expression of RORγt gene and protein were downregulated by hp-MSCs intervention.Conclusion Reduction of placental hp-MSCs levels is an independent risk factor for infant bronchiolitis. The balance of TH17/Treg is managed by hpMSCs through upregulation of Foxp3 protein and gene expression,downregulation of RORγt protein and gene expression as well, it is further raised the increase of antiinflammatory cytokine secretion,and decrease of inflammatory factor secretion.