Mature cystic teratoma of the ovary is one of the most common ovarian neoplasms found in reproductive age woman. The most common type of malignancy associated with ovarian mature cystic teratomas is squamous cell carcinoma. Malignant transformation rarely take place in this tumor, and is observed in approximately 1% to 2% of all case. The frequency of this type of malignant degeneration is age related and is most common in fourth and sixth decade of life. We have recently experienced a case of squamous cell carcinoma arising from the benign cystic teratoma of the ovary in unmarried, virgin, a 40-year-old Korean woman.