To analyze the expression trends and clinical significance of Apurinic/Apyrimidinic Endodeoxyribonuclease 1 (APE1/Ref-1) and Nucleophosmin (NPM1) proteins in high-grade serous ovarian adenocarcinoma (HGSC). The expressions of APE1/Ref-1 and NPM1 proteins in 94 patients with HGSC were determined using the immunohistochemical (IHC) method, and their relationships with clinicopathological features were analyzed by the chi(2) test or Fisher's exact test. The follow-up data, Cox proportional hazards univariate and multivariate survival analyses were integrated to evaluate the prognostic factors affecting patients with HGSC. In the normal fallopian tubes, APE1/Ref-1 and NPM1 protein were mainly distributed in the nuclear. The HGSC experienced changes in the cellular localization of APE1/Ref-1 and NPM1 protein expressions, which were abnormally expressed in the cytoplasm. The rates of abnormal cytoplasmic expression of APE1/Ref-1 and NPM1 proteins in 94 patients with HGSC were 69.1% and 73.4%, respectively, which were significantly higher than the normal fallopian tube tissues (p < 0.05). The abnormal cytoplasmic APE1/Ref-1 and NPM1 are significantly correlated with the lymph node metastasis, chemosensitivity, FIGO staging, and prognosis. The COX multivariate survival analysis showed that the abnormal expression of APE1/Ref-1 protein, FIGO staging, and lymph node metastasis are independent prognostic factors. Collectively, the abnormal cytoplasmic APE1/Ref-1 and NPM1 proteins are associated with the oncogenic progression and chemoresistance of HGSC, and predict a poor prognosis.