Aim: To measure the levels of interleukin-18(IL-18) in the serum of patients with acute coronary syndrome (ACS) and explore its relation with ACS. Methods:The serum concentrations of IL-18 were measured in 31 patients with ACS including 12 patients with acute myocardial infarction (AMI group) and 19 patients with unstable angina pectoris(UAP group)by enzyme-linked immunosorbent assay (ELISA). Fifteen patients with stable angina pectoris (SAP group) and 16 controls without coronary diseases were used as control. Results: Serum IL-18 levels in AMI and UAP groups were significantly higher than those in SAP and control group (P0.01). Serum IL-18 levels in SAP group were significantly higher than those in control group(P0.01).Conclusion: Level of serum IL-18 can reflect the stable status of coronary atherosclerosis plaque. IL-18 can be a serum marker to predict the occurrence of ACS.