This study investigated the physical development and identified obesity risk factors of children in two primary schools in Dong Anh district in Hanoi. Methods: A cross-sectional study was conducted involving 492 school children of Dong Hoi and Thuy Lam primary schools in Dong Anh district, Hanoi city from November, 2011 to April, 2012. Results: The data showed that children of overweight parents had a greater risk of becoming obese than lean parents. School children having one overweight parents or both overweight parents were 3.5 and 6.7 times more likely to be overweig.ht themselves than children with normal weight parents. The authors also identified that greedy, fast eating, over eating, and extra meals were some of the risk factors of these overweight school children. Over eating is the greatest risk factor that contributed to 6.0 times more risk of being overweight, followed by fast eating (3.8 times), extra meals (2.9 times), and greedy for food (2.5 times). Extra consumption of high fat content food (2.2 times), sugary food (2.6 times), and less consumption of vegetables and fruit (2.0 time) also contributed to children obesity. Regular physical activity reduced the risk of overweight and obesity. School children with less physical activity had 2.1 time higher risk of overweight and obesity than children with regular physical activity.