Objective: Epithelial ovarian cancer (EOC) is the leading cause of female mortality in gynecologic malignancies, with a rising incidence in Japan. This study aimed to validate the treatment patterns and safety of niraparib as maintenance therapy for EOC following initial chemotherapy in clinical practice in Japan. Methods: Leveraging claims data between April 2008 and December 2022, this descriptive study comprised EOC-diagnosed patients receiving initial platinum-based chemotherapy, debulking surgery, and niraparib as maintenance therapy. Patient characteristics, prescription status, transfusion details, and laboratory data were assessed and reported as summary statistics and frequencies. Results: Among 291 patients, the median age was 64.0 years and 94.5% received a 200-mg daily dose of niraparib. At week 12, 78.7% (229/291) continued niraparib treatment, 21.3% (62/291) discontinued, and 52.2% (152/291) required treatment interruptions. Of the 62 patients who discontinued treatment, 27 patients initiated subsequent EOC treatment within 12 weeks following niraparib discontinuation. Blood transfusions were needed in 10.3% (30/291), and of 55 patients with available laboratory data, 61.8% (34/55) had decreased platelet count <100,000/µL, 25.5% (14/55) had decreased hemoglobin level <8 g/dL, and 22.7% (5/22) had decreased neutrophil count <1,000/µL, meeting the criteria for treatment interruption. Among those with thrombocytopenia, 88.2% (30/34) were able to either resume or continue treatment. Conclusion Niraparib demonstrated favorable tolerability in Japanese patients with advanced EOC, with effective management of thrombocytopenia through dose adjustments and supportive care, supporting its viability as post-chemotherapy maintenance therapy.