A young nulliparous woman with stage IIIC bilateral borderline micro-papillary serous carcinoma (MPSC) of the ovary underwent conservative surgery with optimal preservation of future fertility. The left ovary and a substantial portion of the right ovary were removed. The patient became pregnant at the first IVF cycle attempted after conservative management. A Cesarean section was performed in the 37th week of pregnancy and combined with very precise exploration; there were multiple non-invasive implants on the peritoneal surface and liver, and contra-lateral ovarian tissue was of normal appearance. Abdominal hysterectomy and right oophorectomy were done as a definitive treatment 3 months after the Caesarean section. The patient showed a rapid progression to invasive ovarian carcinoma in this period of time. MPSC has the greatest risk of malignant transformation among the advanced stage serous borderline tumours. Fertility-sparing surgery is an option for young, childless women who would like to preserve their fertility. However, the treatment must be taken very cautiously and requires rigorous surveillance.