Malignant transformation of fibrous dysplasia (FD), which was first introduced by Coley and Steward is very rare. We present a case of malignant transformation of monostotic mandibular FD after 2 surgical excisions, 20 and 15 years ago, respectively. The treatment choice of FD is usually conservative. With the advanced surgical techniques, radical excisions followed by immediate reconstruction have been reported. However, the decision criteria are still controversial and we might think that radical treatment is a good method for recurrent lesions based on the recent literatures. The case discussed here is of sarcomatous transformation of a recurrent FD