Abstract: Objective: To investigate the effects of the lipid raft inhibitor,methyl-β-cyclodextrin(MβCD) on the activation and aggregation of human platelets in vitro.Methods: Human whole blood collected from normal subjects were stood still for 20 min before stimulation with 20 μmol/L adenosine diphosphate(ADP),some groups were pretreated with MβCD before ADP stimulation,and some groups untreated as control.The fibrinogen receptor(FIB-R) positive percentage(%) and its mean fluorescence intensity(MFI),and aggregation percentage(%) of platelets were measured by flow cytometry.Results: In ADP stimulated groups,FIB-R(%),FIB-R(MFI),and aggregation(%) of platelets reached 75.93±10.27,329.19±121.72,and 23.03±4.96,respectively,in comparison with that in the untreated control(66.66±12.58,73.78±21.91,and 2.53±0.72,respectively),the FIB-R(MFI) and aggregation(%) were significant higher(P<0.01).Pretreated with MβCD,three above parameters were 36.92±16.55,40.06±25.48,and 4.09±(2.78),respectively,compared to that in ADP group,there were significantly reduced(P<0.01).Conclusions: MβCD,depleting cellular membrane cholesterol,could obviously inhibit the activation and aggregation of platelets induced by ADP.