The increasing prevalence of childhood obesity and its concomitant health risks justify widespread efforts toward prevention. Although both diet and physical activity have been emphasized as appropriate interventions, the current paper focuses on the role of physical activity in obesity prevention. Children’s levels of physical activity are highly variable, and may be influenced by a multitude of factors including physiological, psychological, sociocultural and environmental determinants. Although the relationship between physical activity and obesity is controversial and the protective mechanism unclear, physical activity is hypothesized to protect individuals from the development of obesity by increasing energy expenditure and resting metabolic rate (RMR) and leading to a favourable fuel utilization. The beneficial effect of physical activity in children is supported by controlled exercise intervention programs. Several broad-based public health interventions designed to increase children’s levels of physical activity have been implemented in schools, families and communities, with results suggesting promising strategies for the prevention of childhood obesity. It is likely that successful prevention of childhood obesity through physical activity promotion will involve theory-based, culturally appropriate school, family and community interventions. Through policy changes, environmental planning and educational efforts in schools and communities, increased opportunities and encouragement for physical activity can be provided.