Abstract: ObjectiveTo study the clinicopathologic features and differential diagnosis of malignant solitary fibrous tumor (SFT) of kidney. MethodsA case of malignant SFT of kidney was examined with gross and light microscopy and immunohistochemistry, with related literature reviewed. ResultsGrossly, the kidney was replaced by a large mass of 20cm×12cm×9cm,poorly circumscribed with the color of grey-white and grey by yellow on the cut surface and multi-foci of necrosis. The diameter of cysts ranged from 0.6cm to 1.0cm. The texture was delicate and tender. Microscopically, alternating hypo-and hypercelluar areas, the tumor was composed of bland spindle-shaped cells, and was col-overlap in hypercellular areas. Mucoid degeneration were in hypocelluar areas. Fine and cluster collagen was within intercyte. The tumor had heteromorphism of low-midddle deree,with numerous mitoses 4 to 6 per 10 high-power fields and multi-foci of necrosis. The hemangiopericytoma-lik structure was scarced, with the area of cystic and fatty degeneration. Immunohistochemical analysis showed that the tumor cells were diffusely positive for Vimentin, CD99, Bcl-2, and meri-positive for CD34 and micro-focus positive for S100. ConclusionThe malignant SFT of the kidney is very rare and the more-than-10cm-diametered tumor may be helpful for assessing malignant SFT. It need to be distinguished from other malignant spindle cell tumors of the kidney. Diagnosis is based on its morphology and immunohischemistry.