Since 1984 we have investigated a method of laserthermia using microprobe in experimental and clinical studies. We reported the advantages and week points of this method that were observed by long term clinical follow-up study, and pursued a new method of laserthermia using balloon for the purpose of overcoming the week points of laserthermia using microprobe. We obtaind the following results: 1) Pathological change of the gastric wall after laserthermia treatments for 18 preoperative patients with early gastric cancer indicated the satisfactory penetration effect and safety of laserthermia. 2) Except for one patient with depressed undifferenciated cancer, biopsy specimens after laserthermia treatments became negative for cancer on 13 inoperable patients aiming for complete eradication of cancer cells by laserthermia. But local recurrence was found on 3 patients who were followed up above 4.5 years after laserthermia treatments. 3) Laserthermia using balloon has several advantages as compered with laserthermia using microprobe.