Purpose: The purpose of this study was to determine the effects of knowledge and attitude on self efficacy of cardiopulmonary resuscitation (CPR) in the fifth and the sixth grade of elementary school students. Methods: The participants were 242 elementary school students from A city. Data were collected from August 26 to August 27, 2013 using a questionnaire. Data analysis was performed by SPSS/WIN 19.0 using ANOVA, t-test, Pearson correlation and stepwise multiple regression. Results: Factors affecting on self efficacy to CPR were attitude (${eta}=.54$), religion (${eta}=-.16$), recognition (${eta}=.15$) and knowledge (${eta}=.13$). These factors explain 47.0% of the variance in self efficacy. Conclusion: The results of this study show that attitude to CPR has the strongest influence on efficacy. Based on the results of this study, we suggest that customized programs and further research by using 2010 guideline are needed to develop for elementary school students.