Abstract: AimTo observe the effect of quercetin (Que) on the adhesion of platelets to cultured endothelial cells and adhesion molecule expression by human umbilical vein endothelial cells(HUVEC) and platelets. Methods［³H］-Adenine labeled platelets were incubated with HUVEC to investigate the effect of Que on adhesion of platelets to HUVEC. The number of platelets adhering to the HUVEC monolayer was determined by liquid scintillation spectroscopy. TNF-α induced HUVEC expression ICAM-1 and thrombin induced platelets expression of P-selectin were measured by flow cytometry. ResultsQue (0.3-2.4 μmol·L－1) was shown to inhibit the increase of P-selectin expression of thrombin activated platelets. Pretreatment of HUVEC with tumor necrosis factor (TNF-α) significantly increased platelets adhesion to HUVEC and the expression ICAM-1. Que (0.6-2.4 μmol·L^-1) inhibited this effect of TNF-α in a concentration-dependent manner. ConclusionQue can inhibit the adhesion of platelets to HUVEC and the expression of adhesion molecules (P-selectin and ICAM-1).