Physical activity (PA) participation plays a key role in preventing and reducing obesity among young children. The preschool years (ages 4-5 years) have been identified as a crucial time to promote PA and prevent the development of obesity. Unfortunately, most school settings offer few opportunities for children to engage in structured PA and few studies have examined the effectiveness of specific PA interventions in this age group. Early childhood PA interventions may help preschoolers establish healthy levels of PA and thereby contribute to the prevention of chronic diseases later in adulthood. Hence there is an urgent need to develop, implement and evaluate potentially effective and innovative PA interventions targeting underserved preschoolers to promote health and cognition among this at-risk population. This project is designed to examine the effects of a 36-week child-led exergaming intervention in promoting underserved preschool children's PA levels and cardiovascular fitness, compared to a traditional PA control group. The project also will investigate the effects of the PA programs on preschool children's cognitive function (e.g., executive functioning), motor skill competence and perceived competence. Additionally, the project will examine the mediating effect of perceived competence on relationships between motor skill competence, PA levels, cognitions and fitness in preschoolers as promoted by the PA programs. A total of 256 preschoolers from 16 schools will be randomly assigned to one of two groups with gender as block: (1) exergaming intervention group (36 weeks of 100 minutes [5 days X20 minutes] exergaming /week); and (2) traditional PA group (36 weeks of 100 minutes [5 days X20 minutes] Mighty Moves /week). Specifically, 64 children will be recruited from 4 schools and randomly assigned to 2 conditions (32 children per each condition) in Year 2, 3, 4, 5 respectively. Preschool children's (4-5 years old) baseline data will be measured at baseline, prior to the start of the 9-month intervention. All children will undergo identical assessments in the 4th month, 9th month and 12th month (follow-up). Outcome variables include: 1) children's daily PA levels, 2) cardiorespiratory fitness, 3) cognitive functions, 4) motor skill competence, 5 perceived competence, and 6) body mass index. Mixed model ANCOVAs will be employed to examine the differences in outcome variables between groups over the course of study. Findings from this project will inform the development of innovative PA programs for preschool children.