The objective of this randomized, clinical trial is to investigate the results of combination platinium based neoadjuvant chemotherapy regimens using gemcitabin/cisplatin or carboplatin/paclitaxelin in advanced stage serous ovarian cancer patients, who have been undergone interval cytoreductive surgery and evaluation of intraoperative and early postoperative complications. In this study, 206 patients with advanced serous ovarian cancer, Figo stage III and IV, and ascites volume more than 500cc which was found by ultrasonography and CT SCAN, and meet the inclusion/exclusion criteria will be recruited and randomly assigned into intervention groups. Histologic diagnosis will be made by paracentesis. The patients in the first group will receive gemcitabin/cisplatin but those in the second group will receive carboplatin/paclitaxel. First, in each group, chemotherapy is done for three cycles, then interval cytoreductive surgery is carried out and primary outcome measures will be evaluated with the measurement of preoperative CA-125 levels, diameter of target lesions, the volume of residual tumor , the volume of ascites , amount of bleeding during surgery, surgery duration and death during surgery .