Cancer is one of the major health problems that induces severe stress, loss of self - esteem and lower morale of cancer patients. Nurses have direct responsibility in developing nursing therapeutics in order to promote of positive perceived illness, self-esteem and morale of cancer patients. Thus, supportive counseling was developed by the researcher. The purpose of this quasi-experimental study was to examine the effects of supportive counseling, which was developed under Existential Counseling Theory, on perceived illness, self-esteem, and morale of cervical cancer patients undergoing radiotherapy. The conceptual framework of this study was derived from Lazarus and Folkmans Stress, Appraisal and Coping Theory (Lazarus & Folkman,1984). The sample comprised of 60 cancer patients who were purposively selected during their therapies at Siriraj hospital from April to October, 1993,They were voluntary participated in a pretest-posttest control group design with informed consent. Demographic data were obtained from the subjects in both groups. The first 30 subjects were designed to be a control group, and the later 30 subjects were designed to be an experimental group. Chi-square test, T - test, Correlation,and ANCOVA analyses were used to test the hypotheses in accordance with qualitative data analysis. The results revealed that in experimental group, the subjects showed significantly higher scores on perceived illness, self-esteem and morale at post-supportive counseling and those prior to supportive counseling. Furthermore, it was found that perceived illness, self-esteem and morale of the experimental group were significantly better than those of the control group. In contrast, it was shown that in the control group, the subjects had significantly lower scores on perceived illness, self-esteem and morale at the end of radiotherapy as compared to those at the beginning. In addition, from qualitative data it was indicated that the both groups perceived cancer and radiotherapy in a negative perspectives which produced depression mood, feeling of hopelessness and anxious behavior at the beginning of the study. However,toward the end of radiotherapy, subjects in the experimental group who received supportive counseling, showed much better feelings regarding their perceived illness and radiotherapy. An active, co-operative, and effective coping behavior was obviously observed which indicated a positive way of adaptation. In contrast, subjects in the control group demonstrated negative and worse feelings regarding their perceived illness, and in turn, showed a more depressive, hopeless and anxious behavior. As the result of the study, it is suggested that nurses should integrate a supportive counseling into the conventional nursing care for cancer patients undergoing radiotherapy continuously, which will improve the patients self-esteem, morale,mental health and adaptation for their better living.