We experienced two rare case of ovarian neuroendocrine carcinoma (NEC); case 1, NEC associated with mucinous adenocarcinoma and dermoid cyst; case 2, NEC with mucinous cystadenoma. The former patient was not treated with chemotherapeutic therapy for her own initiative and died of the tumor extent ten months after surgery. The latter patient has taken an uneventful clinical course for ten years after surgery with chemotherapy. To our knowledge, there have been limited documents regarding ovarian NEC to date. No proper subclassification is not assigned to NEC in the current WHO classification of ovarian tumors. According to the certain investigators, the postoperative survival term of ovarian NEC considerably differs. The therapeutic protocols including chemotherapy and irradiation have not been established yet. In most ovarian NECs, histogenesis is considered to be associated with mucinous or teratoma tumor which coexists with NEC.