Twenty six cases of borderline ovarian tumor(BOT) were treated between Jan. 1985 and Dec. 1997 at the Department of Obstetrics and Gynecology, Hanyang University. The clinical records were reviewed for all patients including histopathology, clinical features, and follow-up. The frequency of BOT was 12%(26/214) of epithelial ovarian malignancies, and patients with these tumors tend to present at a younger age(36 yrs) than those with invasive carcinomas. In terms of histologic type, mucinous type(21/26: 81%) were more prevalent than serous tumor(5/21: 19%) in this study. The positive rate of CA 125 was 20% in serous, and the positive rate of CA 19-9 was 24% in mucinous tumor. The size of mucinous was larger than that of serous tumors(17.1 cm vs 9,3 cm). Almost all of these tumor categorized as early stage(stage I: 96%), however, only one patient with serous tumor had advanced stage of disease(stage III: 4%), Therefore BOT tend to be diagnosed as earlier than invasive carcinoma. About 2/3 of patients were treated as conservative surgery(unilateral salpingooophorectomy or enuclation). Postoperative adjuvant chemotherapy was not given about half of cases(13/26). Median follow-up was 43 months and recurrent case was found only one in serous tumor, All patients in this study are still alive and free of disease except one, 5-year survival rate was 100%. But large number of study and long-term follow-up are needed to make a decision to treat and manage of BOT.