Five cases of ovarian cancer are presented in which malignant squamous cell elements were present. Three of the cases were adenosquamous carcinoma without composite endometriosis, mature cystic teratoma or with mixed mesodermal tumor. The other two cases were squamous cell carcinoma which arose in mature cystic teratoma, one of them being in situ carcinoma. Among cases of adenosquamous carcinoma, one composed predominantly of squamous cell element and foci of endometrioid adenocarcinoma was found. In this case, transitional figures between the two components were found. In other cases of adenosquamous carcinoma, components of adeno- and squamous cell carcinoma were intermingled in each carcinoma cell nests. Thus a large variety of histogenesis and microscopic figures were seen in malignant squamous cell elements in the ovarian cancer.