Purpose: The purpose of this study was to examine the mediation of self-efficacy in the relationship between anger and the functional health of homeless men in order to provide a basis for planning nursing interventions to improve the functional health of homeless persons. Methods: The participants were 137 homeless men who lived in homeless shelters or visited one center serving free meals for homeless persons in Seoul. Data were collected using self-report questionnaires and analyzed with the SPSS-WIN 20.0 program. The instruments were the Functional Health Pattern Screening Assessment Tool (FHPAST), Self-efficacy Scale (SES), and State-trait Anger Expression Inventory-Korean version (STAXI-K). Results: The mean score for functional health was 2.41. Overall self-efficacy was 70.82. state anger was 16.53, trait anger was 19.54, and anger expression was 25.31. There were signigicant correlations among the 3 variables, functional health, self-efficacy, and anger. Also, self-efficacy had a complete mediating effect in the relationship between anger and functional health. Conclusion: Based on the findings of this study, health management programs focusing on anger management and self-efficacy improvement are highly recommended to promote functional health in homeless persons.