Purpose: This study was done to identify the relationships between body mass index, nutritional knowledge and the health promotion behavior of nursing students. Methods: Participants consisted of the entire 330 members of the student body of a Korean nursing college. Variables included body mass index, nutritional knowledge and health promotion behavior as well as demographic variables. Data was analyzed by frequencies, ANOVA and Pearson’s correlation with the SPSS/Win 21.0 program. Results: The mean score for body mass index was 20.23 kg/m2 for nutritional knowledge, 14.27±3.07 on a total 20-point scale, and for health promotion behavior, 3.03±0.34 on a 4-point scale. Nutrition knowledge positively correlated with health promotion behavior (r=.368, p<.001). Health promotion behavior positively correlated with underweightness (r=.120, p=.005), normal weight (r=.212, p<.001), negatively correlated to overweightness (r=-.351, p<.001), and obesity (r=-.413, p<.001). Nutrition knowledge positively correlated to underweightness (r=.155, p=.005), and normal weight (r=.346, p<.001), negatively correlated to overweightness (r=-.548, p<.001), and obesity (r=-.342, p<.001). Conclusion: In order to enhance the effective health promotion behavior of nursing students, it is important to actively intervene to improve body weight control behavior and nutritional knowledge. Therefore, developing an educational program for improving nutritional knowledge and body weight control behavior of nursing students is recommended.