The Benign mucinous cystadenomas account for 16-30 percent of all ovarian neoplasms. Of these, the giant variant occurs rarely. A 26-year-old woman with abdominal distension was diagnosed by computerized tomography and ultrasound having a huge cystic ovarian tumor. At laparotomy, there was a 35 cm sized cystic mass of the right ovary. Right salpingo-oophorectomy was performed. We experienced a case of huge mucinous cystadenoma of right ovary with high serum levels of CA125 and CA19-9, and report this case with a brief review of concerned literature.