This study was done to investigate the changes in the quality of life(QOL) of patients who received radiation therapy after surgery for breast cancer. For this purpose, 35 patients were interviewed using a questionnaire. They were followed over 8 month period from the beginning of radiation therapy. Changes in the QOL, side effect of the RT(radiation therapy), depression were measured. The results can be summarized as follows : 1. The mean score of the side effect of RT increased significantly over the period of RT. When the RT was completed, the QOL score was the low-est, and the depression score was the highest, but the changes of these scores were not statistically significant. 2. When the 6-week RT was finished, the QOL was significantly correlated with QOL of the beginning of RT, depression at RT completion and age. At three months after the completion of RT, the QOL was significantly correlated with QOL of the beginning of RT, depression and side effect of RT at three months after the completion of RT. At six months after the completion of RT, the QOL was significantly negatively correlated with age. 3. In the stepwise multiple regression analysis, the major influencing variables on the QOL were various according to the time lapse after the RT. The QOL at the completion of RT was predicted by the QOL at the beginning of RT, depression at the completion of RT and age. The QOL at three months after the completion of RT was predicted by the QOL at the beginning of RT and side effect of RT and depression at three months after the completion of RT. The QOL at six months after the completion of RT was predicted by age. This study suggests that continuous nursing care be required for improving the QOL of breast cancer patients not only during the RT period but also for a long term after the completion of RT.