〔Abstract〕 Objective To investigate the mechanism of quercetin inhibiting proliferation of prostate cancer cells(LNCap) by regulating promoter methylation of glutathione S transferase P1(GSTP1).Methods Human prostate cancer LNCap cells were cultured in vitro,and treated with quercetin( 0,10,40,80 μmol/L) and methyltransferase inhibitor 5'-aza-dc( 10 mol/L) as the control group. After 48 h,CCK-8 method was used to detect the inhibition rate of cell proliferation in each group. Cell apoptosis was detected by flow cytometry. Methylation status of GSTP1 gene was determined by methylation specific PCR( MSP). MRNA and protein expression of GSTP1 in LNCap cells were detected by real-time PCR and Western blot. Results The proliferation rate of LNCap cells decreased with the increase of quercetin dosage and time in a certain concentration range( P<0. 05). The methylation of GSTP1 promoter in LNCap cells decreased( P<0. 05). The expression level of GSTP1 increased( P<0. 05). Moreover,the decrease of GSTP1 m RNA was negatively correlated with the methylation of GSTPl gene( P<0. 05). Conclusion Quercetin inhibited the growth and proliferation of LNCap cells by reducing the methylation of LNCap promoters.