Alveolar soft-part sarcoma (ASPS) is rare. We present a case of a 30-year-old woman with a 6-month history of a palpable mass in her left thigh. MRI showed an 8-cm mass and a satellite nodule at the left gluteus muscle. The main tumor exhibited an isointense signal on T1-weighted images and high-signal-intensity areas with low-signal-intensity scanty solid components on T2-weighted images. MR angiography showed dilated and tortuous veins around the tumor. Histologic findings were compatible with ASPS.