Abstract： Objective To evaluate the feasibility and efficacy of optical coherent tomography (OCT) in differential diagnosis and treatment of pulmonary vascular diseases. Methods OCT system (Lightlab, US) was used to scan 16 pulmonary vessels with diameters ranging from 2 mm to 6 mm in 10 patients with vascular stenosis and/or occlusion (after prior interventional revascularization) confirmed by pulmonary arteriography, followed by measurement and analysis with the built-in software of the system.Results Sixty- six OCT scans were performed for 16 pulmonary vessels in 10 patients, generating characteristic images in all the cases without any complications. Manifestations in OCT scans included pulmonary thromboembolism (n=5) with normal arterial wall thickness, red or white thrombus adhering to intima and stenosed lumen; idiopathic pulmonary hypertension (n=3) with pulmonary arteries 2 mm to 6 mm in diameter, disappearance of normal 3-layered structure of vessel wall, granulation and incrassation of intima, increased reflection, lumen stenosis ＞ 50%, and minimum inner diameter of lumen no more than 1 mm; pulmonary arterial occlusion of unknown reason (n=2) with normal or thickened intima, fibroid hyperplasia 0.17 mm to 0.60 mm by thickness, fistulous adherence to intima causing 60%-80% occlusion of lumen. Post- interventional revascularization of pulmonary arterial occlusion and/or stenosis: incomplete intima, subintima lipid plaques, multiple lesions with fracture of plaques, fragmented intima, red and white thrombus, and formation of local dissection. Conclusion OCT can be safely performed in various phases of pulmonary arterial diseases, and may demonstrate characteristic histological changes of vessel wall in different pulmonary angiopathy, facilitate diagnosis and differential diagnosis, and guide the therapy of pulmonary arterial diseases.