Although majority clinical trials of antiplatelet therapy in patients with acute coronary syndrome(ACS) showed significant benefits, but in elderly patients, especially ≥75 years, the outcomes mostly were less effective, the bleeding risk increased. This review will discuss briefly the pathobiology of hemostasis, thrombosis and hemorrhage due to aging, and the changes of vascular repair and integrity, and the clinical benefit and bleeding risk of antiplatelet therapy in elderly patients with ACS in recent clinical trials.