Aim Thrombelastography for evaluating the antiplatelet efficacy of clopidogrel and ticagrelor in the patients with acute coronary syndrome（ACS） and Type 2 diabetes mellitus undergoing PCI. Methods Eighty-seven patients with ACS and diabetes undergoing PCI were randomized into two groups. The patients of clopidolgrel group（n92） were preoperatively given in loading aspirin 300 mg and clopidogrel 300 mg, followed by 100 mg aspirin and 75 mg clopidogrel per day. The patients of ticagrelor group（n88） were preoperatively given in loading aspirin 300 mg and ticagrelor 180 mg followed by 100 mg aspirin per day and 90 mg ticagrelor twice one day. We investigated platelet reactivity （AA inhibition rate and ADP inhibition rate） by thrombelastography, and observed ischemic of cardiac and bleeding events over 3 months. Results Ticagrelor group had low rate of MA-ADP pathway（%） compared with clopidogrel group（34.94%±11.91% vs 47.16%±14.90%，P<0.001）. For the inhibition rate in AA pathway（%） and inhibition rate in ADP pathway（%）,ticagrelor group was superior to clopidogrel group （68.24%±22.96% vs 48.21%±32.91%，58.16%±23.52% vs 33.34%±26.67%，P<0.001）. Conclusion Ticagrelor had more power to inhibit platelet reactivity compared with clopidolgrel in patients with ACS and diabetes undergoing PCI. Ticagrelor reduced ischaemic events during 3 months, without increasing bleeding events compared with clopidogrel.