Purpose : To observe changes in side effects and fatigue of the cancer patients receiving radiation therapy on the head/neck and the chest over a period from the start to the end of the therapy, and to analyze correlation between side effects and fatigue. Method : Twenty seven patients receiving radiation therapy 5 days per week for longer than 6 weeks participated in the present study. Fatigue was measured for when healthy, before-, and after-therapy. Side effects was surveyed by structured questionnaire on the last day of each therapy. Result : The results of this study were as follows. 1. Major side effects of the head/neck patients were skin irritation, change of taste, sore throat and xerostomia, while the chest patients experienced fatigue, skin irritation, anorexia, difficulty swallowing and cough increased with therapy. 2. Although fatigue was significantly changed for when healthy and before-therapy (F=60.25, p <.05) and also for before- and after-therapy, no statistical significance was demonstrated in fatigue of both the chest head/neck patients (p> .05). 3. Fatigue and side effects showed high correlation form the 4-th week with after the therapy Conclusion : The present results could be of great use to develop systematic intervention technique, leading to practical help for patients, since side effects and fatigue change to a large degree depending on the disease and the timing and technique of the therapy.