We aimed to identify the effect of an extended number of neoadjuvant chemotherapy (NAC) cycles on prognosis and surgical morbidity after interval debulking surgery (IDS) in patients with newly diagnosed advanced ovarian cancer. Medical records of patients with advanced ovarian cancer treated with NAC and having undergone IDS were retrospectively reviewed. Clinicopathological factors were compared between two groups: conventional (≤4 cycles) and extended (≥5 cycles) NAC groups. Kaplan-Meier analysis was performed to evaluate progression-free survival (PFS) and overall survival (OS). A total of 156 patients were included, 112 patients in the conventional group and 44 patients in the extended NAC group. The extended NAC group had a significantly higher frequency of cancer antigen (CA)-125 normalization after NAC (59.1% vs. 33.9%, P = 0.004), a lower rate of bowel surgery (18.2% vs. 34.8%, P = 0.042), and a lower rate of transfusion during or after IDS (36.4% vs. 59.8%, P = 0.008) as compared to the conventional group. The complete cytoreduction rate after IDS was similar between the groups. In multivariate Cox regression analysis for PFS, radiologically stable and progressive disease after NAC (Hazard ratio HR, 1.983; 95% Confidence interval CI, 1.141-3.446; P = 0.015) and gross residual tumor after IDS (HR, 2.054; 95% CI, 1.414-2.983; P < 0.001) were independent risk factors for poor PFS. However, extended NAC cycles were not significantly associated with poor PFS. The median PFS was 19.5 and 16.9 months (P = 0.830), and the 5-year OS was 71.4 and 63.2% (P = 0.677) in the conventional and extended NAC groups, respectively. Our study showed that extended NAC cycles were not inferior to conventional NAC cycles in terms of survival in patients with advanced ovarian cancer and reduced surgical morbidity such as bowel surgery and transfusion during or after IDS.