Neuroendocrine carcinoma and adenocarcinoma existing in the stomach simultaneously is extremely rare. This report presents a 65-year-old male patient who was diagnosed with three types of malignant tumors in the stomach, neuroendocrine carcinoma (NEC), moderately differentiated adenocarcinoma and mucinous adenocarcinoma. In addition, the NEC and moderately differentiated adenocarcinoma existed in the same lesion and, therefore, was referred to as a mixed adenocarcinoma - NEC tumor. The patient underwent laparoscopic-assisted D2 radical total gastrectomy, Roux-en-Y esophagus-jejunum anastomosis and received FOLFOX chemotherapy for six cycles 3 weeks after surgery. Follow-up determined that the patient survived and was tumor-free 12 months after surgery. In conclusion, radical surgery combined with chemotherapy can effectively improve the prognosis of patients with these three specific tumor types simultaneously in the stomach.