The study was to evaluate the role of intravascular ultrasound (IVUS) in assessment of coronary artery stenosis, lesion morphology and guidance of percutaneous left main coronary artery intervention. 16 patients with left main coronary artery lesions evaluated by IVUS were involved in the study. The data showed that the average MLA is 7.29 + or - 3.0 mm2 in left main lesion sites and 3.88 + or - 1.44 mm2 in ostial LAD lesion sites. The average plaque burden' is 62 percent at lesion site. With drug eluting stent, the trend is to cover as much disease as possible (stent length is longer than lesion length). Fourteen (14) patients with left main lesion sites and 12 with ostial LAD lesion sites were qualified for stent placement intervention. After PCI stent placement, the average MLA is improved significantly from 7.29 + or - 3.0 mm2 to 12..88 + or - 5.2 mm2 (p 0.0001) for left main lesions, and 3.88 + or - 1.44 mm2 to 8.28 + or - 2.19 mm2. In conclusion, intravascular ultrasound (IVUS) is beneficial for the assessment of lesion morphology and guidance of percutaneous left main coronary artery intervention.