Objective:To explore the role of ERK signal pathway in the extracellular matrix(ECM) synthesis of rat mesangial cells treated with PDGF-BB in vitro. Methods:Cultured rat mesangial cells were divided into seven groups:control cells; treated with PDGF-BB(10,25,50 ng/ml,respectively);treated with PDGF-BB(25 ng/ml) and UO126(5,10 -滋mol/ml,respectively);treated with UO126 10 -滋mol/ml. The expression of fibronectin(FN),matrix metalloproteinases-2(MMP-2) and plasminogen activator inhibitor-1(PAI-1) mRNAs were detected by RT-PCR. Results:In mesangial cells,PDGF-BB downregulated MMP-2 mRNA expression(P < 0.05),upregulated PAI-1and FN mRNAs expression in a dose-dependent way(P < 0.05). The changes of FN,MMP-2 and PAI-1 mRNA induced by PDGF-BB can be inhibited by UO126 in a dose-dependent fashion(P < 0.05). Conclusion:PDGF-BB can inhibit the degradation of extracellular matrix and stimulate the synthesis of FN in rat mesangial cells through ERK siginal pathway.