Immunoglobulin G4-related disease (IgG4-RD) is characterized by extensive infiltration of IgG4(+) plasma cells and fibrosis in various organs. However, the involvement of the ovary in IgG4-RD has never been reported. A 59-year-old woman presented with urinary retention. Magnetic resonance imaging and computed tomography revealed a huge multinodular pelvic mass and common iliac/para-aortic lymph node swelling. A laparotomy was performed under the suspicion of advanced ovarian cancer, and the pelvic mass was identified as ovary in origin. Histopathology of the excised tumor revealed massive lymphoplasmacytic infiltration (>90% were IgG4(+) plasma cells), storiform fibrosis, and obliterative phlebitis; thus leading to a diagnosis of IgG4-RD. We conclude that IgG4-RD can present as a bilateral ovarian mass along with lymphadenopathy, therefore mimicking ovarian cancer.