Abstract: Objective: To investigate the effect of homocysteine(Hcy) on ECV-304 cells growth and to probe into a possible mechanism by which hyperhomocysteinemia (HHCY) results in atherosclrosis.Methods: ECV-304 cells were incubated with media containing a range of concentrations of Hcy for different time,changes in the morphology of cells were observed under microscope;thiazolyl blue tetrazolium bromide(MTT) assay was performed to examine the growth inhibitory rate of cells; ³H-TdR incorporation test was used to examine DNA synthesis of ECV-304 cells.Results: ECV-304 cells were identified by their typical cobblestone morphology when viewed by light microscope in control group,but the arrange of cells became disorderly,congregate with the increase of concentration of Hcy and the extension of time in test groups.No difference was found among 0.1,1.0,2.5 mmol/L Hcy groups and control group,but incubation with 5.0,10.0 mmol/L Hcy produced a significant inhibitory effect compared with control group (P<0.05-P<0.01).Treated with 5.0 and 10.0 mmol/L Hcy for 48 hour and 72 hour,the inhibitory rate at 72 hour was significantly higher than that at 48 hour(P<0.01).Incubation with 5.0,10.0 mmol/L Hcy for 48 hour,and 72 hour,the inhibitory rate of DNA synthesis was significantly increased than that in control group and low concentration groups(P<0.05-P<0.01);and the inhibitory rate of groups which were incubated with 5.0,and 10.0 mmol/L Hcy for 72 hour,was higher than that for 48 hour group(P<0.01).Conclusions: Hcy had a direct injurious effect on ECV-304 cells,and an inhibitory effect on the growth and DNA synthesis of ECV-304 cells in time- and concentration-dependent manner.