Abstract: Malignant mesenchymoma (MM) is a a kind of soft tissue sarcoma composed of two or more different types of malignant mesenchymal components with a low incidence. The authors reported a special case of MM, which occurred in lung and was found by ¹⁸F-FDG PET/CT examination. The features of MM were analyzed from clinical symptoms, laboratory examinations, imaging findings and related literature reports, in order to deepen clinicians' understanding of lung MM.