Fibrous dysplasia is a benign disease which develops slowly over a few years and it's cause is unknown. The incidence of this disease is 2.5% of whole bone tumors and 7% of benign bone tumors. Most common site is maxillary bone in the facial bones, therefore maxilary bone changes to abnormal shape, produce mass appearance, and develops symptoms. The polyostotic type is rare compared to the monostotic type. The author reports one case of polyostotic fibrous dysplasia occurred in both maxillary sinuses.