Abstract: Objective To observe the efficacy and safety of ticagrelor treated on patients with low clopidogrel response.Methods A total of 173 of 493 patients undergoing percutaneous coronary intervention(PCI)with acute coronary syndrome(ACS) were selected as low colpidogrel response identified by thrombelastography and enrolled in this study. Patients with low clopidogrel response were randomized into clopidogrel treated group(n=87) and ticagrelor treated group(n=86). Patients responding to clopidogrel were still treated with clopidogrel(75 mg daily)and patients with low clopidogrel response received ticagrelor treatment(90 mg twice daily). Platelet aggregation rate was compared between two groups after treatment for 3 days, 7 days and 30 days. All patients were followed 12 months for major adverse cardiovascular events(MACCE) and bleeding events.Results Patients in ticagrelor treated group showed significantly lower platelet aggregation rate compared with patients in clopidogrel treated group after 3 days, 7 days, and 30 days (P<0.05). Patients in ticagrelor treated group showed significantly lower MACCE rate compared with patients in clopidogrel treated group in the postoperative 12 months' follow-up(P<0.05). There were no significant difference in bleeding events(P＞0.05).Conclusion Ticagrelor therapy can achieve ideal antiplatelet effects for patients with low clopidogrel response. For the patients with low clopidogrel response receiving PCI, ticagrelor can be an effecive and safe choice for antiplatelet therary.