86-year-old lady who presented with history of abdominal distension for few years was transferred from local clinic. She complained of mild abdominal discomfort with especially dull sense on lower abdomen. On her physical examination, huge, hard in consitency and immobile mass was palpable on her whole abdomen. Abdominal CT demonstrated with huge ovarian malignant tumor more the 25 cm in its diameter with large amount of ascites. On PET-CT, about 30 cm sized malignant mass probably originated from ovary with possible carcinomatosis peritonei but no metabolic metastasis was presented. Based on these predictive feature of malignancy on image studies, we decided to go for an operation giving a thought to the mass as an ovarian malignancy. During the operation, huge mass which weighed 5400g presented severe adhesion with atrophied uterus which only weighed 80g. Large amount of ascites was seen, however no definite metastatic lesions were observed. Post-operative histopathological analysis confirmed the huge mass as benign fibroma of ovary. According to the 2003 WHO histological classification, ovarian cellular fibrous tumors are defined to present with mitotic figures 3 or less per 10 HPF and no severe nuclear atypia. Clinicopathologic characteristics of fibromas of ovary can mimic malignancy, therefore, it should be differentiated carefully in correlation between the radiologic and pathologic findings. We found the case remarkable in its unusual outcome that huge ovarian mass in such a dimension which turned out to be benign fibroma.