Aim To investigate the endothelial function and platelet activation during myocardial ischemia-reperfusion injury and the protective effect of magnesium. Methods Thirty-two rabbits were randomly divided into four groups. In control group the left anterior descending coronary artery (LAD) was falsely ligated. In ischemia group the LAD was ligated. Rabbits in reperfusion group and therapy group underwent 0.5 h of LAD occlusion and 4 h of reperfusion. After LAD ligation rabbits in therapy group were intravenously given magnesium sulfate and rabbits in the rest groups were given 0.9% sodium chloride. The level of plasma Mg 2+, nitric oxide (NO) and the number of alpha-granule membrane protein-140 (GMP-140) molecule on platelet surface were measured before LAD ligation and after ischemia for 0.5 h, reperfusion for 1 h and 4 h. Results ①The plasma concentrations of Mg 2+, NO and the number of GMP-140 molecule on the platelet surface in control group were of no statistical difference before and after false LAD ligation (p>0.05); ②The level of Mg 2+, NO were significantly decreased and the number of GMP-140 molecule on platelet surface was increased after myocardial ischemia/ischemia-reperfusion in ischemia group, reperfusion group compared with those before LAD ligation and those at the same time in control group (p<0.05); ③The level of Mg 2+,NO was increased and GMP-140 was decreased in therapy group compared with those in ischemia group and reperfusion group (p<0.05). Conclusions It suggests that there is endothelial dysfunction and platelet activation during ischemia-reperfusion. Sulfate magnesium might be useful in protecting endothelium and inhibiting platelet activation.