True aneurysm of the pulmonary vein (PVA) is a very rare, but it may occur as an isolated congenital defect in vessel wall. Acquired PVA was rarely seen associated with mitral insufficiency and dilated left atrium with mitral insufficiency. A 70-year-old man was consulted to an outpatient department due to solitary pulmonary nodule on simple chest radiograph. Medical history was unremarkable for trauma, congenital cardiac disease, systemic vasculitis, and syphilis but he was treated with type 2 diabetes and essential hypertension for 7 years. On physical examination, the lungs were clear and there were no cardiac murmurs. Laboratory tests were within normal ranges. Echocardiogram was normal findings with no specific valve abnormalities or vegetations and no chamber enlargements. Pulmonary function tests were demonstrated normal ventilation. Spiral chest CT showed 2 cm sized fusiform structures with strong enhancement. It was characterized direct connection to the pulmonary vein, and it was encased by the 3.5 cm sized round pneumatocele in the in the same section of lung setting in the superior segment of right lower lobe. Since the CT findings were absolutely clear, angiography was not performed. Under the diagnosis of PVA originated from right inferior pulmonary vein wedge resection was done. And pathologic diagnosis was compatible with about 3.5×1.5 cm sized venous aneurysm encased in lung cyst. Herein, we report a very interesting and extremely rare case of dilatated pulmonary venous aneurysm encasing simple lung cyst in asymptomatic patient.