Mature cystic teratoma (MCT) accounts for 30-45% of all ovarian tumors. Malignant transformation of these tumors is a rare event ,which develops only in 1 to 2% of the cases. But it must be highlighted that though it may be a rare occurrence, malignant transformation is associated with a poor prognosis. Of all transformations, squamous cell carcinoma (SCC) is the most common histological type accounting for about 75% of all malignant transformations. We hereby report a case of a 49 year old female with mass in abdomen for 3 months associated with pain. Ultrasound studies suggested an ovarian tumor-solid cystic teratoma. Total abdomimal hysterectomy with bilateral salphingo oopherectomy was done. Moderately differentiated invasive squamous cell carcinoma arising in a background of mature cystic teratoma was diagnosed by histopathological studies.