Objective To investigate the effects of Tirofiban on the expression of matrix metalloproteinase(MMP-9)and sCD40L in patients with acute coronary syndrome(ACS)after percutaneous coronary intervention(PCI)and to explore the potential mechanism of anti-artherosclerosis and stabilize plaque by Tirofiban.Methods Eighty-six patients with ACS were enrolled and were randomly divided into the control group and the Tirofiban group with different time periods after PCI.The expression of MMP-9 and sCD40L were tested by ELISA at 6 h,12 h,24 h,36 h after PCI.Results After application of Tirofiban 6 h,12 h,24 h,36 h,the expression of MMP-9 decreased from(228.25 ±0.015)ug/L to(53.56 ±0.02)μg/L and the expression of sCD40L decreased from(321.12 ±0.02)ng/L to(123.32 ±0.02)ng/L,compared with the control group,the difference was significant(P ＜ 0.05).Conclusions Tirofiban can inhibite the expression of sCD40L and MMP-9,the inhibition of the expression of MMP-9 may be related to the CD40/CD40L pathway.This effect may be one of the mechanism of reducing atherosclerotic plaque inflammation and preventing plaque rupture by Tirofiban.