Aim To discuss the effect of soy isoflavones (Genistein and Daidzein) on preventing the oxidation of LDL mediated by Cu 2+ and to investigate the effect of Genistein on c myc mRNA expression induced by ox LDL in human vascular endothelial cells (ECV304). Methods 1. LDL were isolated from healthy human plasma by gradient ultra centrifugation and oxidized by Cu 2+ . The formation of TBARS and relative electrophoretic mobility were employed to measure the antioxidant activity of Genistein and Daidzein of different concentrations (50, 100 and 200 μmol/L respectively). 2. LDL isolated from healthy human plasma by gradient ultra centrifugation and oxidized by Cu 2+ was used as a stimulus. ECV304 cells were exposed to ox LDL (200 mg/L) in the presence or absence of Genistein 100 μmol/L for 1, 2 and 4 h in vitro. Northern Blot was employed to measure c myc mRNA levels of the treated cells. Results 1. The formation of TBARS and relative electrophoretic mobility of LDL were inhibited by Genistein in a concentration dependent manner (p<0.05 vs control); However, Daidzein made none senses compared with control on the formation of TBARS and relative electrophoretic mobility of LDL (p>0.05). 2. In response to ox LDL 200 mg/L, c myc mRNA expression of hUVEC increased by about three folds in 1 2 h and decreased below the control level at 4 h; Genistein 100 μmol/L effectively inhibited this over expression both at 1 and 2 h. Conclusions Genistein not only prevents the oxidation of LDL but also inhibits the over expression of c myc mRNA induced by ox LDL in ECV304.