This study investigated the effects of acute exercise on cognitive function and the modulatory role of fitness in the relationship between exercise and cognition. Forty-six healthy older adults, categorized into higher or lower fitness groups, completed the Stroop test after both 30 min of aerobic exercise and a reading control with a counterbalanced order. Our findings demonstrated that acute exercise leads to general improvements in 2 types of cognitive functions and to specific improvements in executive function. Additionally, older adults with initially higher fitness levels experienced greater beneficial effects from acute exercise.