Primary pulmonary malignant fibrous histiocytoma (MFH) is very rare, so only a few imaging features have been reported. We report one case of rapidly growing primary pulmonary MFH mimicking a partially thrombosed pulmonary artery aneurysm and its radiologic findings, including multidetector row computed tomography (MDCT), conventional angiography, and fluorodeoxyglucose-positron emission tomography CT ([18F] FDG-PET/CT). On multi-phasic MDCT, this mass mimicked a pulmonary artery aneurysm with partial thrombosis. However, pulmonary artery aneurysm was excluded and suggested as a hypervascular parenchymal mass by subsequent conventional angiography. On [18F] FDG-PET/CT, it was a highly metabolic mass, showing a maximal standard uptake value (SUV) 12.1. Although primary pulmonary MFH is very rare and has no specific imaging findings, our experience might be helpful to differentiate a hypervascular pulmonary mass.