Background: Prognostic value of tumor regression grading (TRG) after neoadjuvant chemotherapy (NAC) in patients with FIGO stage IIIC epithelial ovarian cancer (EOC) is controversial. Methods: A total of 55 stage IIIC EOC patients who underwent interval debulking surgery (IDS) after NAC at the Department of Gynecology of Liaoning Cancer Hospital and Institute between January 2003 and September 2016 and had full information were involved this retrospective study. All the pathological sections were individually reviewed by two pathologists. TRG was determined by the ratio of viable tumor versus fibrosis, ranging from TRG 0 when no viable tumor, to TRG 5 when fibrosis was absent. TRG 1 was defined as regression more than 75%, TRG 2 was defined as regression more than 50% but less than 75%, TRG 3 was defined as regression more than 25% but less than 50%, and TRG 4 was defined as regression less than 25%. Patients were stratified into TRG 0-1-2 group and TRG 3-4-5 group according to cut-off values calculated through receiver operating characteristic (ROC) curves. Progression-free survival (PFS) and overall survival (OS) were analyzed using Kaplan-Meier method. Univariate analyses were performed using log-rank tests. Multivariate analyses were performed using Cox regression analysis to assess the prognostic factors of TRG, which were expressed as hazard ratios (HRs). Results: Univariate and multivariate analyses suggested that TRG and residual disease (RD) were independent predictive factors of PFS, and TRG, RD and CA125 change were independent predictive factors of OS. TRG was a better prognostic factor compared with CA125 value change after NAC (area under curves [AUC] of the ROC of TRG 0.93 versus AUC of the ROC of CA125 change 0.69). The median PFS of the patients in TRG 0-1-2 group was 14.0 months longer than TRG 3-4-5 group (26.0 months versus 12.0 months, HR 2.19, 95% confidence interval [CI] 1.17-4.07, P = 0.014). The median OS of the patients in TRG 0-1-2 group was 28.6 months longer than TRG 3-4-5 group (50.4 months versus 21.8 months, HR 3.10, 95%CI 1.49-6.42, P = 0.002). Conclusions: TRG after NAC was an independent prognostic factor of patients with FIGO stage IIIC EOC.