Abstract: AIM To observe the effect of clopidogrel or ticagrelor on platelet aggregation in patients with acute coronary syndrome(ACS) and type 2 diabetes mellitus(T2DM). METHODS A total of 175 patients with ACS and T2DM in Wuhan Asia Heart Hospital were included in this retrospective study. Patients were divided into two groupsticagrelor group(n=22) and clopidogrel group(n=153). Platelet aggregation function was tested by light transmission platelet aggregation(LTA) and the difference of platelet aggregation function between groups was compared. RESULTS No significant difference was found between groups in arachidonic acid(AA)-induced platelet aggregation rate(32±20)% in clopidogrel group and(26±17)% in ticagrelor group(P=0.160). Adenosine diphosphate(ADP)-induced platelet aggregation rate in ticagrelor group was lower than clopidogrel group(40±18)% vs.(51±18)%, P=0.01. CONCLUSION Ticagrelor significantly decreases ADP-induced platelet aggregation rate moreso than clopidogrel in patients with ACS and T2DM, but no significant difference is found in AA-induced platelet aggregation between drugs.