We describe a malignant granular cell tumor in the semimembranosus muscle of a 61-year-old woman. Magnetic resonance images disclosed a tumor with intermediate and low signal intensity on both T1- and T2-weighted images, measuring about 7 x 4 x 4 cm in size. The patient showed an uneventful clinical course during a 30-month follow-up period after the wide excision. The pertinent findings in making the diagnosis of malignant granular cell tumor are large size, intramuscular location, and mitosis including an atypical mitosis.