A growing body of research has illuminated beneficial effects of a single bout of physical activity (i.e., acute exercise) on cognitive function in school-age children. However, the influence of acute exercise on preschoolers' cognitive function has not been reported. To address this shortcoming, the current study examined the effects of a 30-min bout of exercise on preschoolers' cognitive function. Preschoolers' cognitive function was assessed following a single bout of exercise and a single sedentary period. Results revealed that, after engaging in a bout of exercise, preschoolers exhibited markedly better ability to sustain attention, relative to after being sedentary (p = .006, partial eta square = .400). Based on these findings, providing exercise opportunities appears to enhance preschoolers' cognitive function.