Purpose: The purpose of this study was to develop an obesity management program for obese children and examine its effects on body composition, self-efficacy, and health promotion. The obesity management program was based on a KAP & HBM mixed model and consisted of health education and group playing exercises. Method: This study was implemented at one elementary school in K city for a total of 12 weeks. The study subjects were a single group, and their body composition, self-efficacy, and health promotion were assessed at both pre-treatment and post-treatment. Data were analyzed by Wilcoxon Signed Rank Test using SPSS WIN 20.0. Result: After the program, the average height of subjects increased by 0.9cm (p=.001), whereas BMI decreased by $0.64kg/m^2$ (p=.003), obesity index decreased by 3.79% (p=.003), and body fat decreased by 1.34% (p=.002). There were significant effects on diet self-efficacy (p=.027), exercise self-efficacy (p<.001), and health promotion (p=.001). Conclusion: This obesity management program reduced the degree of obesity and improved self-efficacy and health promotion. Therefore, the obesity management program is an effective intervention method for elementary-aged obese children.