Fifty-four cases of ovarian mucinous cystadenoma, including two cases containing ciliated cells representing the müllerian epithelial origin, one case admixed with serous adenoma component and six cases associated with mature teratoma, were examined for the demonstration of gastrointestinal characteristics using periodic acid-Schiff, alcian blue, galactose oxidase-Schiff, paradoxycal concanavalin A (ConA), Grimelius and Fontana-Masson stains. Of 41 endocervical-type mucinous cystadenomas not associated with teratoma, 34 cases (83%) showed ConA positivity, expressing gastrointestinal characteristics. As both cases with ciliated cells and the case with serous adenoma component exhibited ConA positivity, the ovarian surface epithelium is supposed to undergo mucinous metaplasia possessing gastrointestinal characteristics. As to the histogenesis of the ovarian mucinous tumors, the metaplasia theory is suggested.