Primary leiomyosarcoma of the inferior vena cava (IVC) is a rare and fatal disease. Imaging is the main diagnostic method. CT and MRI images of IVC leiomyosarcoma have been published, but ultrasonographic features have been scarcely described, especially with contrast-enhancement. We report the case of a patient in whom ultrasonography incidentally revealed a mass in the IVC. Contrast-enhanced ultrasonography showed heterogeneous enhancement in the arterial phase with some irregular non-enhanced areas, and mild clearance in the venous phase. The location and nature of the lesion as shown by ultrasonography were confirmed by CT and MRI.