Abstract: AIM: To study the effect of quercetin on TNF_α induced endothelialneutrophil adhesion and its mechanism. METHODS: Cell adhesion was measured by testing neutrophil myeloperoxidase activity; expression of adhesion molecules was measured by ELISA. RESULTS: The adhesion rate of unactivated human umbilical endothelial cells (EC) to neutrophils was very low. TNF_α(100～1000 kU·L^-1) increased the adhesion of EC to neutrophils both doseand timedependently. Quercetin(1～500 μmol·L^-1) dosedependently inhibited the adhesion of TNF_α stimulated EC to neutrophils. The expression of ICAM-1 and VCAM-1 on the surface of resting EC was very low and no Eselectin expression was detectable. TNF_α increased the expression of these adhesion molecules and resulted in upregulation of endothelialneutrophil adhesion. CONCLUSION: Quercetin inhibited TNF_αstimulated endothelialneutrophil adhesion by suppressing the expressions of ICAM-1, VCAM-1 and E-selectin.