Background: Personal resources are one of the determinants of lifestyle and health. The aim of the research was to analyze the relationship between sense of generalized self-efficacy, and body mass index (BMI), diet health quality and health behaviors of female nursing students and active professional nurses. The analyzed variables in the group of students and nurses were also compared. Material and Methods: The study was conducted among a group of 269 women (174 students and 95 nurses working at hospitals), using: the Beliefs and Eating Habits Questionnaire (KomPAN), Juczyński’s Health Behavior Inventory (HBI) and the Generalized Self-Efficacy Scale (GSES). The BMI was assessed on the basis of anthropometric measurements. Statistical calculations were performed using analysis of variance, the Student’s t-test, multivariable regression analysis and Pearson’s correlation as well as moderation analysis, with the adopted level of statistical significance at α = 0.05. Results: Professionally active nurses achieved higher BMI levels (25.95 vs. 22.31 kg/m², p < 0.001) and a higher non-healthy diet index – nHDI-14 (17.04 vs. 15.00, p = 0.038) than students. It was shown that with the increase in generalized self-efficacy (GSE), diet health quality and the level of positive mental attitude, proper eating habits and the overall index of health behaviors increased. The BMI increased with the rise in the non-healthy diet index and with the decline in health behaviors (individual categories and the overall index). It was not found that the group (students vs. working nurses) was a moderator of the relationships between health behaviors and indicators of diet health quality with GSE of the studied nurses (p > 0.05). Conclusions: Nurses with a higher sense of self-efficacy declared a higher diet health quality and healthier behaviors, and their BMI was related to diet quality and health behaviors. Med Pr Work Health Saf. 2023;74(4):251–61.