Metastatic gastric cancer is uncommon, and metastasis of colorectal cancer to the stomach is extremely rare. We report a case of metastatic gastric cancer that originated from transverse colon cancer. A 52-year-old woman underwent a left hemicolectomy and D3 lymph node dissection based on a diagnosis of transverse colon cancer. The pathology results were as follows: mucinous adenocarcinoma, type 2, 6 × 11 cm, ss, ly1 v1, pm (-), dm (-), n1 (+), P0, H0, M0, Stage IIIa. The patient received XELOX as postoperative adjuvant therapy for 6 months. One year and 3 months after the left hemicolectomy, gastroscopy revealed a submucosal tumor in the lower body of the stomach and an incipient cancer in the cardia of the stomach, and a colonoscopy revealed an incipient cancer in the transverse colon. An endoscopic ultrasonography fine needle aspiration biopsy of the submucosal tumor in the lower body of the stomach was performed. Histology showed that this tumor was a mucinous adenocarcinoma similar to the primary transverse colon cancer, which led to a diagnosis of metastatic gastric cancer originating from transverse colon cancer. Distant metastasis was not detected. Endoscopic submucosal dissection of the incipient gastric cancer was performed, as were distal gastrectomy and partial colectomy. Peritoneal dissemination and para-aortic lymph node recurrence were detected 7 months after the second surgery.