Malignant giant cell tumors of bone (MGCTB) are rare, and the diagnosis can be difficult due to the occurrence of a variety of malignant tumors containing giant cells. To better understand its clinicopathological features, we have reviewed our experience with 17 cases of MGCTB. Five cases were primary malignant giant cell tumor of bone (PMGCTB), and 12 cases were giant cell tumors of bone initially diagnosed as benign but malignant in a recurrent lesion (secondary MGCTB, SMGCTB). The patients included six women and 11 men (age ranged from 17 to 52 years; mean, 30.5 years). The tumor arose in the femur (six cases), the tibia (seven cases), the humerus (three cases), and the fibula (one case). Microscopically, PMGCTB showed both conventional giant cell tumor and malignant sarcoma features. SMGCTB were initially diagnosed as conventional giant cell tumor of bone, the recurrent lesion showing malignant features. Histologically, the malignant components included osteosarcoma (11 cases), undifferentiated high-grade pleomorphic sarcoma (two cases), and fibrosarcoma (four cases). SMGCTB cases showed strong expression of p53. Follow-up information revealed that four patients died of lung metastasis, two patients are alive with lung metastases, and 11 patients are alive without tumor. MGCTB should be considered as a high-grade sarcoma. It must be distinguished from GCTB and other malignant tumors containing giant cells. p53 might play a role in the malignant transformation of GCTB.