A man in his 60s received SP (S-1+CDDP) therapy for gastric cancer with multiple liver metastases. After completion of 3 courses, liver metastases had reduced significantly, and the paraaortic lymph nodes, which had swelled previously, had reduced in size. Furthermore, the serum carcinoembryonic antigen (CEA) level had also improved to the standard value from 814.3 ng/mL. The patient was able to discontinue the opioid he had needed for pain control. The chemotherapy was continued for 18 courses, with the dose reduced at the time of the adverse events along the way. By completion of the 18 courses, we recognized regrowth of the primary lesion and a rise in the serum CEA over the standard value. There was no sign of the regrowth of liver metastases and distant lymph nodes according to examinations for enhanced computed tomography (CT) and ¹⁸F-fluorodeoxyglucose positron-emission tomography (FDG-PET) CT.The patient received distal gastrectomy. The CEA level decreased in standard value or less after surgery and we believed the cancer was limited to the primary stomach lesion.