Carcinoembryonic antigen (CEA) in plasma is useful for the detection of recurrent colonic or gastric cancer and the monitoring of plasma in patients with recurrent cancer displaying therapeutic effect. We report a sharp decline of CEA in a patient with recurrent gastric cancer by 6 months oral administration of UFT. The patient was an 81-year-old male who had undergone gastrectomy for advanced gastric cancer. Eight months post-operatively, the plasma CEA began to rise logarithmically, and recurrent tumor in the remnant stomach and liver metastasis were detected by fibergastroscope (FGS) and abdominal CT. After administration of UFT at a dose of 300 mg per day, CEA abruptly declined logarithmically and normalized in 6 months. Presently marked reduction of recurrent foci and metastases were found by FGS and abdominal CT. Therefore sequential changes in plasma CEA in this patient can be considered to reflect the effect of therapy for recurrent gastric cancer by UFT.