Background <p>The positive correlation between physical activity and cognitive function has been increasingly documented, while the underlying mechanisms remain unclear.</p> Methods <p>This study aimed to investigate the association among physical activity (PA), functional fitness, and cognitive function in community-dwelling older adults, and to examine whether functional fitness mediates this association. This study utilized a cross-sectional design, encompassing 224 participants aged 65 or above, with 41.07% male and 58.93% female. The data were collected in 2023 using the Mini-Mental State Examination, Physical Activity Scale for the Elderly, and Senior Fitness Test. Pearson correlation analysis was conducted to assess associations among the variables, and mediation analysis was performed using the PROCESS macro for SPSS.</p> Results <p>The results indicated that PA had a moderate positive correlation with cognitive function (<i>r</i> = 0.437, <i>p</i> &lt; 0.01) and with most functional fitness domains. In addition, significant positive correlations were found among most functional fitness domains and cognitive function. The association between PA and cognitive function was partially mediated by cardiorespiratory endurance (Effect = 0.0519, 95% CI= [0.0205, 0.0889]).</p> Conclusion <p>This study demonstrated a positive correlation between PA and cognitive function in older adults, with cardiorespiratory endurance mediating this association. Our study provides valuable preliminary evidence that cardiorespiratory endurance exerts a mediating role between PA and cognitive function. Future longitudinal research is warranted to elucidate the causal relationship and underlying mechanisms between PA and cognitive function.</p>