Abstract: Objective To observe the effects of aspirin on vascular endothelial cell proliferation in vitro and on the activity of p44/p42 mitogen-activated protein kinase (MAPK) phosphorylation. Methods ECV 304 cells cultured in vitro were treated with aspirin (1, 2, 5, and 10 mmol/L, respectively) and observed for their proliferation in comparison with the control group. The ratio of cell proliferation was determined by non-radioactive MTS/PES assay. The expression of phosphorylated p44/42 MAPK protein was evaluated by the immunoblotting technique using anti-p44/42 phospho-MAPK antibody. Results The proliferation rate of the endothelial cell was 1.533±0.286 in the control group, and 0.459±0.107, 0.708±0.125, 0.953±0.149 and 1.253±0.225 in aspirin-treated groups corresponding to aspirin concentrations of 10, 5, 2 and 1 mmol/L, respectively. It was shown that aspirin significantly inhibited the vascular endothelial cell proliferation at the concentration above 1 mmol/L (P<0.05), in a dose-dependent manner as compared with the control group (P<0.05). The expression of phosphorylated p44/42 MAPK protein was significantly inhibited by aspirin. Conclusions Aspirin decreases vascular endothelial cell proliferation, and arrest of endothelial cell proliferation may be an important mechanism by which aspirin produces protective effect against acute coronary disease.