The majority of choriocarcinomas occur in the uterus as gestational malignant tumors. Rarely, a choriocarcinoma appears in the gastrointestinal tract, and the tumor is assumed to arise from a different histogenetic origin as compared to tumors of other sites. A primary gastric choriocarcinoma is a rare aggressive, widely metastatic malignant tumor, and has a poor prognosis. Reported here is a case of a 69-year-old woman with a primary gastric choriocarcinoma who presented with melena, epigastric pain, and was diagnosed with a poorly differentiated adenocarcinoma based on a preoperative endoscopic biopsy. Gastrectomy with lymph node dissection, followed by postoperative chemotherapy, is the treatment of choice. Therefore, in the case of a poorly differentiated adenocarcinoma with a bleeding tendency, a meticulous examination with the suspicion of a choriocarcinoma should be undertaken.