Background OCT is a new intravascular imaging method with high resolution. Objectives The aim of the present study was to evaluate the ability of OCT for assessment of atherosclerotic plaque characteristics and vulnerability in patients with ACS compared to SCAD patients. Methods and results Patients undergoing cardiac catheterization were enrolled and categorized into: recent ACS, or SCAD. OCT imaging was obtained using the commercially available Frequency Domain-OCT and the Dragonfly catheter. Two observers independently analyzed the images. Of 48 patients enrolled, 27 with ACS, and 21 with SCAD. In the ACS, and SCAD groups, lipid-rich plaque (was observed in 96.3%, and 66.7%, respectively (P=0.015). The median value of the minimum thickness of the fibrous cap was 70, and 100 μm, respectively (P=0.064). The frequency of thin-cap fibroatheroma was 33.3%% in the ACS group, and 14.3% in the SCAD group (P=0.185). No procedure-related complications occurred. Conclusion The current study demonstrated the differences of the culprit lesion morphologies between ACS and stable CAD. There was a trend toward a higher frequency of TCFAs in patients with ACS compared to SAP patients. The morphological feature of lipid rich plaque content, plaque rupture and the intracoronary thrombus could relate to the clinical presentation in patients with acute coronary disease. Plaque erosion was a frequent ﬁnding in patients with ACS not in SCAD patients. This is consistent with previous pathological studies.