In the pre-operative radiation therapy for gastric cancer, radiosensitivity of the tumor, anatomical limit of irradiated field, selection of the patient for this therapy and influence of irradiation to surgical procedures have remained unsolved. For these reasons, this treatment has not been widely used for gastric cancer. We tried to evaluate this therapy by animal experiment and clinical experience. Animal experiment: Radiosensitivity of gastric cancer transplanted to nude mice was measured and compared each other. Higher inhibition of the tumor growth was obtained by 3000 rad irradiation in gastric cancer group. Inhibition of cancer activity was observed on the seventh day after irradiation had started and on the 10th day, all tumor showed remarkable inhibition. Histological destruction of cancer tissue was observed in all cases unrelated to histologic pattern. However, well differentiated adenocarcinoma showed higher sensitivity than poorly differentiated. Clinical aspect: We applied this therapy to the patient with cardiac carcinoma only because of inability of systemic bursectomy and prevention metastasis to the esophagus. Using Linac X-ray, 300rad per day and 4000 rad in total were irradiated. Therapeutical effects and some side effects of this therapy are discussed in this report.