Objective: This study aimed to investigate whether the sleep quality is associated with body composition, selective attention, and autonomic nervous system (ANS) activity in healthy young individuals.Methods: This cross-sectional study was conducted using the Korean version of Pittsburgh Sleep Quality Index (PSQI-K). Sixteen healthy volunteers aged 20–26 years participated in this study. The PSQI-K was used to evaluate sleep quality, and they were divided into good and poor sleeper groups by PSQI-K. Body composition, and both reaction time and error number for discriminative reaction task indicating the selective attention, and ANS activity were measured and it compared according to sleep quality. Additionally, the correlation between sleep quality and ANS activity was analyzed.Results: There were no significant differences in the body composition, reaction time and error number between good and poor sleeper groups. In the ANS activity, the poor sleeper group only showed the lower HF value than the good sleeper group in resting state (p=0.023). Whereas, the amount of change (reaction task state – resting state) in mean HR (p=0.005), HF (p=0.039), and LF/HF ratio (p=0.023) were significantly different between the groups. Additionally, a negative correlation was observed between PSQI-K and HF (p=0.005), while a positive correlation was confirmed between PSQIK and LF/HF ratio (p=0.012).Conclusion: These findings indicate that even healthy individuals may have physiological problems such as ANS imbalance if the sleep quality is poor.