Pulmonary artery aneurysms are extremely rate and are seldom diagnosed during life. In true aneurysms, dilatation tends to be confined to the main trunk of the artery and degenerative changes in the wall are found. In 1971, Williams et al reported the first successful excision and replacement of the main pulmonary artery, including the bifurcation, with a dacron graft. Since then there have been few cases of main pulmonary artery aneurysm treated surgically. However, aneurysm of the main pulmonary artery treated surgically was not reported in our country till now. Recently we have experienced a case of the mainpulmonary artery aneurysm in a 10 years old boy and it was confirmed by echocardiogram, ultrasonogram of the chest, computed tomogram of the chest, radioisotope heart scan, cardiac catheterization and cine-angiogram of main pulmonary artery, aorta & right ventricle etc and patent ductus arteriosus was noted at the indifferent site from aneurysmal sac. Thereafter he underwent surgical correction at our hospital with the aid of total cardiopulmonary by-pass.