Objective To observe the effect of rat bone marrow mesenchymal stem cells(BMSCs)on the apoptosis of rat peritoneal mesothelium cells(PMCs)induced by high glucose peritoneal dialysis fluid(PDF),and to explore its possible molecular mechanism.Methods The primary BMSCs and PMCs were extracted and identified.Apoptosis of PMCs was induced by high glucose PDF.Cell supernatant from BMSCs after 24 h of culture was collected as the conditioned medium(BMSCs-CM).PMCs were co-cultured with BMSCs by conditioned media or Transwell chambers.PMCs were randomly divided into the control group,the PDF group and the PDF+BMSCs-CM group.The viability of PMCs was measured by CCK-8 in each group.The depolarization of mitochondrial membrane potential was measured by JC-1 method.TUNEL staining was used to detect cell apoptosis.Western blot assay was used to detect the expression levels of apoptosis related proteins B-cell lymphoma-2(Bcl-2),Bcl-2 associated X protein(Bax),Cleaved cysteine aspartase-3(Cleaved Caspase-3)and pathway related protein serine/threonine protein kinase(Raf),mitogen-activated extracellular signal-regulated kinase(MEK),extracellular-signal regulated protein kinase(ERK)and their phosphorylated proteins in each group.Results Compared with the control group,the proliferative activity and mitochondrial membrane potential of PMCs were decreased in the PDF group,while the apoptosis rate and the ratio of Bax/Bcl-2,Cleaved Caspase-3/Caspase-3,p-Raf/Raf,p-MEK/MEK and p-ERK/ERK were increased(P＜0.05).Compared with the PDF group,the proliferative activity and mitochondrial membrane potential of PMCs were increased in the PDF+BMSCs-CM group,while the apoptosis rate and the ratio of Bax/Bcl-2,Cleaved Caspase-3/Caspase-3,p-Raf/Raf,p-MEK/MEK and p-ERK/ERK were decreased(P＜0.05).Conclusion BMSCs can reduce the apoptosis of PMCs induced by high glucose PDF,and its mechanism maybe related to inhibiting the activation of Raf/MEK/ERK signaling pathway.