Abstract: Objective: To observe the effect of homocysteine on the production of nitric oxide(NO) and reactivated oxygen species (ROS) in ECV-304 cells.Methods: ECV-304 cells were incubated with different of concentrations of Hcy for 24 hours.A nitric-acid reductase method was used to detect NO in different groups with and without three stimuli of nitric oxide synthase(NOS),and ROS in cells was detected by flow cytometry(FCM).Results: After cells were exposed to 0.5 mmol/L,1 mmol/L Hcy for 24 hours,NO in cultured media was significantly less than that in control group (P<0.01).Employing three stimuli for NOS,Hcy still resulted in a gradual decline in NO,and 1.0 mmol/L Hcy produced a statistical suppression of NO (P<0.01) compared with low concentration groups and control group.When incubated with 0.5 mmol/L,1.0 mmol/L Hcy fluorescence in cells detected by FCM was higher than that in control and low concentration groups (P<0.01).Conclusions: Hcy can dose-dependently restrain the excretion of NO and promote the production of ROS.