This study was to assess knowledge, practices and attitude on overweight and obesity of the pupils in Ngo Sy Lien secondary school, Hoan Kiem district, Hanoi. Results showed that the proportion of pupils had knowledge on causes of obesity was 86.9 percent, a consequence of obesity was 82.9 percent, control method of obesity was 83.7 percent. The feeling of pupils when suffered from obesity (sad, ashamed...) accounted 73.1 percent and attitude for your friends with obesity (funny, don't care...) were 7.1 percent. The rate of the pupils played computer games was 52.9 percent. The proportion of pupils had snack at night was 21.1 percent, drinking beverage 2 - 3 box/week was 26.7 percent and 3-4 box/week was 14.7 percent. In conclusion, knowledge of the pupils on obesity were quite good, however practices of the pupils on obesity could not acceptable. These findings may provide basic data for dieticians in order to develop effective nutrition interventions for school pupils.