We present a rare case of main pulmonary artery stenosis secondary to protruding fibrous material in the main pulmonary artery associated with patent ductus arteriosus. A 1-month-old baby boy manifested cardiac murmur. Echocardiogram showed circumferential high echogenic mass inside the main pulmonary artery with pressure gradient of 49 mmHg and patent ductus arteriosus. The mass did not regress during 3 months' follow-up period. Angiographic images showed that the circular filling defect was located at the main pulmonary artery distal to pulmonary valve, and pulmonary valve and both pulmonary arteries were normal. After surgical removal of the circumferential material and ductus ligation, the pressure gradient became negligible. The material was consisted of scarcely cellular fibrous tissue, abundant coagulum of fibrinous material and dense calcification.