Background: Several studies have shown that plaque characteristics of acute myocardial infarction (AMI) was different compared with that of chronic stable angina. The time of symptom onset and clinical presentation might be important factors in assessing coronary lesion of AMI. The aim of this study is to evaluate the difference of plaque characteristics between early and late stage in patients with AMI by IVUS. Methods: Pre-intervention and post-stenting IVUS was performed in 53 patients of AMI. Patients were divided into an immediate (average 6.2 hours) or early period (average 7 days) on the basis of time of symptom onset. We evaluated the quantitative IVUS parameters as well as qualitative IVUS parameters (incidence of low hypoechoic thrombus, bright speckled plaque, plaque rupture, echolucent area, arterial remodeling pattern, calcification, instent thrombosis) in the both groups. Results: See below. Conclusion: The bright speckled plaque, which may be one form of thrombi, was frequently observed at the presenting time of AMI. However, other plaque characteristics were not significantly changed between immediate and early period in patients with AMI.