Background and Objectives; Shoulder of atheromatous plaque is known as weak site for plaque rupture (PR). However, there is little report whether plaque shoulder is truly weak site for PR in in-vivo study. Subjects and Methods; We evaluated 22 patients who had PR at the culprit lesion by virtual histology-intravascular ultrasound (VH-IVUS). The site of ruptured plaque is divided by cross-sectional view (center, shoulder, undetermined) and longitudinal view (proximal, middle, distal). Results; PR was found in center (n=11), shoulder (n=8) and undetermined (n=3) by cross-sectional view. Longitudinal view showed that PR was developed in proximal (n=10), middle (n=8) and distal (n=4) portion of the plaque. PR in the center of the plaque had higher plaque area (18.2짹3.7mm2 vs. 11.4짹3.0mm2, p=0.000), fibrous area (8.7짹2.5mm2 vs. 4.5짹1.4mm2, p=0.001), fibrofatty area (2.5짹1.0mm2 vs. 1.6짹1.1mm2, p=0.016) and plaque burden (74.0짹8.3% vs. 63.5짹10.2%, p=0.023) than in the shoulder group. Multi-vessel disease was higher in middle and distal group (proximal; 20%, middle; 75%, distal; 75%, p=0.037). PR was frequently found in the proximal 1/3 in left anterior descending coronary artery whereas diffusely distributed in right coronary artery. Conclusion; PR is mostly occurred in proximal and middle of the plaque by longitudinal view and equally developed both in center and shoulder of the plaque by cross-sectional view in patients with acute coronary syndrome. Keywords: Plaque rupture, Acute coronary syndrome, Ultrasonography, Interventional.