Mature cystic teratoma (MCT) of ovary is most common germ cell tumor. The malignant transformation of the MCT is very rare and it occurs only in 1 to 2% of the cases. most common malignancy that can arise is Squamous Cell Carcinoma (SCC).Most of the time, the pre–operative diagnosis will be dermoid cyst of ovary; only histopathological examination of resected specimen and careful sampling of solid area, known as Rokitansky tubercle will reveal the hidden malignant transformations of MCT. We came across one such a rare malignant transformation of MCT in 45year old postmenopausal woman, who attended gynecology department for her chronic abdominal pain and abdominal distension.