Between 1 and 2% of benign cystic teratomas undergo malignant transformation. This occurs most frequently in postmenopausal women, who account for only 10% of benign cystic teratoma. A wide variety of neoplasms arise in the mature tissues of otherwise benign teratomas. Of the malignancies arising in teratomas, squamous carcinoma is the most common (83%) with sarcomas accounting for 7%, adenocarcinoma and carcinoid tumors make up most of the others. The presentation in StageⅠ disease does not differ from that of benign cystic teratoma, except that ascites is occasionally present. In the more advanced neoplasms, the symptoms are those of epithelial ovarian cancer of the same stage. Differential diagnosis between squamous cell carcinoma and benign mature teratoma is difficult but seems to be related to age, size, serum tumor marker (SCC, CA125, CEA). Prognosis of squamous cell carcinoma in mature cystic teratoma was reported much poorer than other epithelial ovarian cancers. In the early stages, treatment is possible through surgical intervention alone, but when advanced, 5 year survival rate shows less than 15 percent. We experienced two cases of squamous cell carcinoma of ovary arising in mature teratoma and present with a brief review of literature.