Background: This study was aimed at investigating the impact of a single exercise intervention on executive function in young adults with Down syndrome (DS). Methods: Considering the relations among executive function, physical and mental health and early onset of Alzheimer's disease in this population, we tested three components of executive function (e.g. choice-response time, attention shifting and inhibition) that have been shown to be impaired in previous studies. Ten persons with DS were assigned to an exercise group, who walked on a treadmill for 20?min at moderate intensity and ten additional persons with DS were assigned to an attentional control group, who watched a video. Measures of executive function were tested pre and post interventions. Results: These results showed non-significant improvements in choice-response time (P?=?0.32) and attention shifting (P =?0.13) but a statistically significant improvement in inhibition (P?=?0.03) after the exercise intervention. Conclusions: Given the improved inhibition ability, exercise may be an effective intervention, even in a signal session. However, only a few studies have focused on this topic. Based on theoretical models linking exercise to executive function, we proposed that exercise may increase arousal status or enhance neural transmission. Hence, future work is needed to examine the exact mechanism in the relationship between exercise and executive function for individuals with DS.