Objective:To explore the effects of Y-box binding protein 1(YB-1) on the proliferation and transforming growth factor-β1 (TGF-β1) secretion in rat mesangial cells (MC). Methods:Rat mesangial cells were cultured with or without YB-1 over-expression,and the supernatant and the cells were collected respectively. The proliferation of MC with YB-1 over-expression was determined by MTT and cell counting. The level of the TGF-β1 protein in the supernatant was mesured by ELISA,while the TGF-β1 mRNA expression was detected by real-time PCR. Results:YB-1 over-expression stimulated the proliferation of MC,upregulated the expression of TGF-β1 mRNA,and induced the TGF-β1 protein secreting in rat MC. Conclusion:YB-1 triggered MC proliferation and increased TGF-β1 secreting,and inhibiting YB-1 expression may be beneficial in retarding progressive development of glomerulonephritis.