AbstractGiant cell tumor (GCT) of the ovary is a rare condition, found almost invariably in the context of a mucinous tumor and presenting a microscopic picture indistinguishable from GCT of bone. Here we describe a case arising from mature cystic teratoma of ovary. An immunohistochemical study was performed using a panel of antibodies to epithelial, mesenchymal and leukocyte antigens. CD68 and vimentin were positive. Along with morphological presence of giant cell and immunohistochemistry findings, Giant cell tumor of ovary was diagnosed arising from mature cystic teratoma of ovary.