Abstract: AIM To explore the role of serum CD40L and matrix metalloproteinses（MMP-s） levels in coronary plague formation. METHODS Fifty-nine (31 men and 28 women, mean age 60.3 years) acute coronary syndrome patients with coronary stenosis confirmed by coronary arteriography were divided into acute myocardial infarction (AMI) group (n=27) and unstable angina pectoris (UAP) group (n=32), and a normal control group (n=30) was set up. The levels of serum CD40L, MMP-2 and MMP-9 were detected by ELISA. RESULTS Compared with those in normal control group, the levels of serum CD40L, MMP-2 and MMP-9 were significantly elevated along with exacerbation of the disease (P<0.01) and the levels of serum CD40L, MMP-2 and MMP-9 in the patients with multiple coronary lesions were higher than those in the patients with single coronary lesion. The levels of serum CD40L, MMP-2 and MMP-9 were positively correlated with that of CD40L (r=0.71 and 0.78, respectively). CONCLUSION The elevation of serum CD40L, MMP-2 and MMP-9 levels are to some extent related to the coronary plague formation. CD40L may cause coronary lesion by way of MMP-s, thus leading to the coronary plague formation and the development of coronary diseases.