In order to examine the injury of vascular endothelial cells related with oxidative stress of reactive oxygen species(ROS), mophological changes of vascular endothelial cells were observed by light microscope after bovine pulmonary vascular endothelial cell line (BPVEC) was treated with 15 uM of hydrogen peroxide. In addition, the effect of vitamin E against ROS-induced oxidative stress was examined by light microscope. In this study, the cell number of BPVEC treated with ROS has significantly decreased than that of control, and the loss of cytoplasmic processes and cell swelling were observed in BPVEC treated with ROS. Whereas, cell number of BPVEC treated with vitamin E has significantly increased than that of BPVEC treated with ROS and also, cytoplasmic processes of BPVEC treated with vitamin E were preserved as control. These findings suggested that not only did ROS induce damage of BPVES by decrease of cell number, loss of cytoplasmic processes and cell swelling, but vitamin E also has protective effect against ROS-induced oxidative stress in cultures of BPVEC.