The cementifying fibroma is mesodermal odontogenic tumor of uncommon occurrence. The authors experienced a case of cementifying fibroma which was developed in the left maxilla and invaded left maxillary sinus of 30 yr old Korean male who admitted to this hospital. The patient first noticed nasal obstruction and mild headache followed by check swelling and protrusion of the hard plate. So he was treated by Caldwell-Luc operation several times without improvement. He had been operated as a cementifying fibroma with improvement. Postoperative follow up was yet uneventful.