Sarcomatous transformation of fibrous dysplasia (FD) is rare and can occur in patients with McCune-Albright syndrome (MAS). To date, there have been several cases of malignant transformation of FD in the craniofacial area of patients with MAS. Here, we report an additional case of secondary osteosarcoma arising from FD in the mandible of a 41-year-old woman with MAS. The patient complained of rapid swelling in the right facial area, which was initially misdiagnosed as soft tissue sarcoma at another hospital. After neoadjuvant concurrent chemoradiotherapy resulting in poor response, the lesion was surgically resected in our hospital, and the final diagnosis of secondary osteosarcoma was rendered. Currently, post-operative adjuvant chemotherapy is in progress. As a result of our review of 17 reported cases showing malignant transformation in FD/MAS, the M/F ratio was 1:1.1, and the median age at onset of malignancy was 28.6 years. The most commonly affected site was the craniofacial bones (n=13; 76%), and the most common histopathologic type of malignancy was osteosarcoma (n=14; 82%). More than half of the patients (8/15; 53.3%) died within 1 year, mainly due to lung metastasis (6/8; 75%). Taken together, since MAS patients with malignant transformation of FD have a relatively poor prognosis, accurate diagnosis based on histopathologic findings as well as clinical and radiographic information is important to select optimal treatment.