Objective To compare the efficiency and safety of clopidogrel of different loading-dose in acute coronary syndromes(ACS) patients with percutaneous coronary intervention(PCI) therapy, and, give an assessment of security about higher loading dose of clopidogrel. Methods 120 patients from January 2008 to January 2009 in our hospital were included.They were randomly divided into 3 groups(na=nb=nc=40)and were given 600 mg,450 mg and 300 mg clopidogrel on the 6 hour before PCI. There was no significant difference between the three groups' basic clinical information(p>0.05),such as age, sex and so on. Four points were selected to observe: the platelet aggregation induced by ADP with 5umol/L before and two hours、four hours, six hours after taking medicine; Primary endpoint events, which include shock during hospitalization, death, target revascularization, myocardial infarction, recurrent angina, stroke in 30 days,and Postoperative Bleeding events and adverse Reactions after Surgery in 30 days. Results compared to the standard dose of 300 mg clopidogrel, 600 mg doses clopidogrel can give a greater degree of inhibition on platelet activating than 450 mg doses in the pre-6 h after administration. Increase Clopidogrel loading dose can reduce the occurrence of major cardiovascular events rate. Bleeding events and the occurrence of adverse events was no significant difference among three groups. Conclusions compared to the standard dose of 300 mg clopidogrel, a higher loading dose of clopidogrel can produce much more faster, greater platelet inhibition, and similar security.