Background: Squamous cell carcinoma (SCC) transformation in mature cystic teratoma of the ovary (MCTO) is a rare but aggressive malignancy, occurring in 1.5%–2.3% of primary ovarian cancers. It predominantly affects postmenopausal women and often presents at an advanced stage due to its asymptomatic progression and nonspecific imaging findings. Optimal diagnostic strategies, treatment approaches, and prognostic indicators remain inadequately defined. Case Description: A 57-year-old postmenopausal woman presented with a two-month history of abdominal pain and distension. Imaging revealed a large, solid-cystic left adnexal mass suspicious for malignant transformation. Staging laparotomy confirmed a 10×9.5×7 cm mature cystic teratoma with SCC transformation, involving the ovarian surface and uterine corpus. The patient underwent total abdominal hysterectomy, bilateral salpingo-oophorectomy, and infracolic omentectomy, achieving R0 resection despite intra operative cyst rupture. She received six cycles of adjuvant paclitaxel-carboplatin chemotherapy and remains in clinical remission 15 months post-treatment. Literature Review: SCC transformation in MCTO is aggressive with poor prognosis, largely dependent on FIGO stage and complete cytoreduction. Preoperative imaging lacks specificity, making early diagnosis challenging. While chemotherapy is beneficial in advanced cases, no standardized regimen exists. Clinical Relevance: This case highlights the importance of early detection, surgical resection, and adjuvant therapy in managing SCC-transformed MCTO. Further research is needed to establish standardized treatment protocols and improve diagnostic accuracy for this rare malignancy