The brenner tumor of the ovary has been the topic of voluminous clinical and pathologic literatures since its original description by Macnaughton Jones in 1898. One of the major problems confronting most investigators of this uncommon neoplasm has been the question of histogenesis. There is general agreement that the tumor is derived from surface epithelium, as are the serous and mucinous cystadenomas. Recently we have experienced a case of Brenner tumor which was found in the wall of a mucinous cystadenoma. A brief review of the literatures and a discussion concerning Brenner tumor are presented in this paper.