A 68-year-old man diagnosed with gastric mixed neuroendocrine-non-neuroendocrine neoplasia(MiNEN)concomitant with liver metastasis received chemotherapy using ramucirumab and paclitaxel. A decrease in tumor marker levels and size of the metastatic liver lesions was observed after 3 courses of treatment. However, the patient developed progressive disease after 9 courses of chemotherapy; hence, nivolumab chemotherapy was initiated. Although liver metastases were reduced after 2 courses of nivolumab, the patient developed new liver lesions after 18 courses of treatment; irinotecan, S-1 and oxaliplatin, and trifluridine/tipiracil were then administered. Liver metastases progressed despite changing the regimen, and the patient died 25 months after the initiation of chemotherapy. Gastric MiNEN usually shows poor prognosis, and there is lack of consensus regarding optimal treatment. Ramucirumab and nivolumab are relatively well-tolerated and may be effective for chemotherapy.