Purpose: The principal objective of this study was to assess correlations among the self-efficacy, social support networks, and health behavior of undergraduate students. Methods: The data were collected via questionnaires that investigated self- efficacy, social support networks, health behaviors, health-related factors, and general characteristics. A total of 310 subjects were selected and evaluated for a 3-week period. The data of 300 subjects were analyzed using descriptive analysis, t-test, ANOVA, and correlation, after 10 questionnaires had been excluded due to incomplete data. Results: We noted significant differences and impacts on self-efficacy according to the grade, perceived health status, and BMI. Social support networks differed significantly according to dwelling type and pocket money. Health behavior differed depending on the gender, major, dwelling type, religion, health status, and BMI. We noted a significant positive correlation between self-efficacy & social support networks, and between social support networks & health behavior, but we noted no significant correlation between self-efficacy & health behavior. Conclusion: Health care providers should focus on self-efficacy and social support networks in order to prevent bad health behavior among undergraduates.