This study was designed to provide the base of nursing intervention that could help apheresis blood-donors to promote self-efficacy effectively by analyzing critical factors that influence on this. The subjects recruited for the research were 468 persons who participated in platelet donation at a university hospital apheresis unit in Seoul. The data for this study were collected between May and June, 2002 using questionnaires. Data were analyzed by t-test, ANOVA, Scheffe test, and stepwise multiple regression. The results were as follows. 1. The mean self-efficacy score on the questions related to blood donation was $32.9pm5.1$, indicating that blood donors have above the mean level of self-efficacy related to blood donation. 2. The self-efficacy score was significantly higher for the group of persons who have more than 5 times of experiences in blood donation than others who have only one experience. 3. The critical factors that influence self-efficacy related to donation were the marital status, educational level. and previous experiences of whole blood donation, while the critical factor that influence on general self-efficacy was previous experiences of whole blood donation. Therefore, it is necessary to establish more effective and organized nursing intervention strategies that can promote the self-efficacy of apheresis blood-donors.