A case of impacted 3rd molar tooth which associated with osteochondroma developed in the right maxillary antrum is to be presented with brief literatures. A 44 year-old female patient visited to our department of Busan Armed Forces General Hospital with complaints of swelling and tenderness of the right cheek. P.N.S. X-ray of the right maxillary antrum showed an adult thumb sized hard mass and tooth like density in the right antrum, but bony destruction sign was not seen. The 3rd molar tooth impacted in the right maxillary antrum and the tumor mass encroached on the anterior wall of the right maxillary antrum were all removed by Caldwell-Luc's procedure. The histopathological finding of the tumor mass was confirmed as osteochondroma.