A 37-year-old woman with an incidentally found abdominal mass was referred to our hospital. A fixed, non-tender mass was palpated in the right upper quadrum of her abdomen. There was no elevation of tumor markers. Computed tomography revealed a mass extending from the hepatic vein level to renal hilar level. The tumor completely obstructed the inferior vena cava (IVC). T1-weighted magnetic resonance imaging (MRI) showed that the mass was isointense with muscles. T2-weighted MRI image with contrast medium demonstrated collateral circulation. Upon diagnosis of the IVC tumor, we removed the right kidney and the tumor en bloc without reconstructing IVC. The tumor diameter was 11.6 × 5.5 × 4.7 cm. Pathological examination established a diagnosis of IVC leiomyosarcoma. She is alive without sign of recurrence after operation for seven months. There were 143 reports of IVC leiomyosarcoma in Japan. In 31% of them, IVC was not reconstructed.