Objective <p>To explore the relationship between Physical Fitness Index and sleep quality in adolescents and to provide a theoretical basis for improving adolescent sleep quality.</p> Methods <p>A total of 5018 adolescents aged 13–18&#xa0;years were selected by whole group stratified random sampling method from September to December 2024 in Changzhi, Taizhou, Jishou, Nanchang, Suzhou, Xianyang, and Yulin, China, for the physical fitness test and sleep quality survey. The correlation coefficients between Physical Fitness Index and sleep quality were analyzed using Pearson's correlation, and the effects of Physical Fitness Index on sleep quality were analyzed using linear regression.</p> Results <p>The total Pittsburgh Sleep Quality Index score was 5.07 ± 3.03 for male adolescents and 5.79 ± 2.95 for female adolescents, with male adolescents significantly better than females (<i>t</i> = -8.61, <i>p</i> &lt; 0.01). The mean value of Physical Fitness Index was -0.70 ± 3.89 for adolescents with poor sleep quality and 0.02 ± 3.70 for adolescents with good sleep quality in the junior high school level, which was statistically different between the two groups (<i>t</i> = -4.058, <i>p</i> &lt; 0.01). Physical Fitness Index was negatively correlated with sleep quality index (<i>r</i> = -0.062, <i>p</i> &lt; 0.01) and Physical Fitness Index significantly predicted sleep quality (β = -0.04, <i>p</i> &lt; 0.01).</p> Conclusion <p>There was a significant negative correlation between the Physical Fitness Index and the Pittsburgh Sleep Quality Index in Chinese adolescents.</p>