PURPOSE: The relationship between physical fitness and cognitive health is not as well documented in younger age groups. Investigations into the relationship between academic achievement and physical fitness have produced mixed results. This study was to investigate the relationship between school academic performance and physical fitness in middle school students. METHODS: The study included a sample of 146 6th-grade students (mean age 11.9±0.4 yrs). After first signing the informed consent, subjects were administered a physical fitness battery conducted by the trained professionals. The academic performance information was collected, including previous and current semester GPA (P-GPA; C-GPA), final GPA for the academic year (F-GPA), ISTEP English scores (IE), and ISTEP Math scores (IM). Only those students with complete sets of scores for both variables were included in the statistic analysis. The relationship between components of physical fitness and academic performance items was examined using correlation coefficient techniques. SPSS for Windows 17.0 was used and a p-value ≤0.05 was considered significant. RESULTS: There was a positive correlation between cardiorespiratory fitness and academic performance with P-GPA (r=0.30, p=0.001), C-GPA (r=0.35, p<0.001), F-GPA (r=0.31, p=0.001), IE (r=0.23, p=0.017), and IM (r=0.20, p=0.039). The agility performance was positively associated with P-GPA (r=0.21, p=0.013), C-GPA (r=0.23, p=0.005), F-GPA (r=0.22, p=0.008), and IE (r=0.19, p=0.030). A positive correlation was found between sit-ups performance and C-GPA (r=0.20, p=0.019), F-GPA (r=0.19, p=0.026) and IE (r=0.19, p=0.025). However, there were negative associations between right handgrip strength and P-GPA (r=-0.21, p=0.012), C-GPA (r=-0.21, p=0.014), and F-GPA (r=-0.23, p=0.005) and between left grip strength and P-GPA (r=-0.18, p=0.034), C-GPA (r=-0.18, p=0.035) and F-GPA (r=-0.18, p=0.029). CONCLUSIONS: The results of this study suggested a high level in cardiorespiratory fitness, agility, and abdominal muscle fitness associating with a high level of academic performance. However, a better performance of handgrip test seemed associating with lower course performance (GPA). Future research is needed on the relationships, cause-effect and mechanisms.