Background Interleukin-18(IL-18) plays a key role in the development, progression and outcome of coronary artery disease and its complications. However, its variability relation to the characterization of atherosclerotic plaque and percutaneous coronary interven- tion are still unknown. Methods Fifty four patients with coronary artery disease [22 patients with stable angina (SA) and 32 patients with acute coronary syndrome (ACS)] were enrolled in this study. All patients underwent percutaneous coronary intervention (PCI). The stability of the plaques at the criminal vessels was assessed with analogical IVUS. Serum IL-18 levels were measured at the time points of 5 min before PCI, and 0h, 6h, 24h and 1month after PCI in all patients. Results ACS group consisted mainly of lipidic unstable plaques while SA group of fibrous stable plaques. Moreover, compared with those in SA group, eccentricity index (EI) and remodeling index (RI) were significantly higher in ACS group. Positive remodeling was seen in ACS group while negative or no remodeling in SA group. Further, serum IL-18 levels were significantly elevated in patients with ACS than those in SA group before PCI, increased at 0h, 6h, 24h after PCI (P<0.05)and were not significant different at 1 month after PCI from those before PCI. Conclusions There is significant difference in the composition and structural characteristics of atherosclerotic plaques between ACS and UA groups. PCI triggersd and enhances the inflammatory response in a short time. Serum levels of IL-18 are the predictors of progression of unstableplaque in atherosclerosis. Post-operative complications of PCI might be reduced by inhibiting IL-18. Background, Interleukin-18 (IL-18) plays a key role in the development, progression and outcome of coronary artery disease and its complications. However, its variability relation to the characterization of atherosclerotic plaque and percutaneous coronary intervention are still unknown. Methods Fifty four patients with coronary artery disease [22 patients with stable angina (SA) and 32 patients with acute coronary syndrome (ACS)] were enrolled in this study. All patients underwent percutaneous coronary intervention (PCI). The stability of the plaques at the Criminal levels were assessed with the time of PCI at all time points of 5 min before PCI, and 0h, 6h, 24h and 1month after PCI in all patients. Results ACS group consisted primarily of lipidic unstable plaques while SA group of fibrous stable plaques. Moreover, compared with those in SA group, eccentricity index (EI) and remodeling index (RI) were significantly higher in ACS group. Positive remodeling was seen in ACS group while negative or no remodeling in SA group. Further, serum IL-18 levels were significantly elevated in patients with ACS than those in SA group before PCI, increased at 0h, 6h, 24h after PCI (P <0.05) and were not significant different at 1 month after PCI from those before PCI. Conclusions There is significant difference in the composition and structural characteristics of atherosclerotic plaques between ACS and UA groups. PCI triggersd and enhances the inflammatory response in a short time. Serum levels of IL-18 are the predictors of progression of unstable plaque in atherosclerosis. Post-operative complications of PCI might be reduced by inhibiting IL-18.