Purpose: This study aimed to investigate the effects of grit and body composition on fatigue and burnout in shift-working nurses. Methods: A descriptive cross-sectional design using self-report questionnaires was employed. Data were collected between February and April 2021 from 192 shift-working nurses in 22 units of C tertiary hospitals. Of the 192, 175 nurses returned their completed questionnaires (return rate: 91.1%). The participants objectively measured their body composition for three consecutive days using a home body composition measurement scale. Results: Nurses with higher consistency of interest were more likely to have lower chronic fatigue (B=-5.23, p=.013), lower emotional exhaustion (B=-2.75, p<.001), and decreased depersonalization (B=-1.08, p=.014). Perseverance of effort was not statistically significant for fatigue; however, it was statistically significant for higher personal accomplishment among the subdomains of burnout (B=2.50, p<.001). Skeletal muscle mass and body mass index had no significant effect on fatigue and burnout. Conclusion: To reduce fatigue and burnout in shift-working nurses, comprehensive efforts at the organizational and individual levels should be implemented to increase their grit. Further research is needed to determine whether body composition affects fatigue and burnout in shift-working nurses.