The effect of Keishi-ka-ryukotsu-borei-to on the prevention of radiodermatitis was examined. Nine cases of lung cancer received radiation therapy with ⁶⁰Co (average 50.3Gy). Three cases were administered Keishi-ka-ryukotsu-borei-to during the therapy. Severe radiodermatitis (abrasion) was manifested only in the control group (4/6). None of the cases where Keishi-ka-ryukotsu-borei-to was administered manifested abrasion. This result suggests that Keishi-ka-ryukotsu-borei-to is effective for the prevention of radiodermatitis.