A 45-year-old woman with papillary carcinoma arising in struma ovarii which involved one ovary without dissemination is presented. Total abdominal hysterectomy and bilateral salpingo-oophorectomy were performed. Histopathological examination revealed malignant struma ovarii of the papillary type. The flow cytometric analysis revealed an hypodiploid DNA content (DNA index:0.67). Since these are rare tumors, there is no universal exact protocol for the treatment and follow-up of patients with malignant struma ovarii. More data are needed to determine the prognosis and management in preferring mode of therapy.