Background: Childhood obesity has become a major public health issue today. The prevalence of obesity and overweight is increasing in both adults and children. Childhood obesity in Thailand has more than doubled since the 1960s and a recent study reported that overweight and obesity in Thais is the 5th highest in Asia. The present study objective was to evaluate the effectiveness of a life-skills, multicomponent, school-based intervention on child nutritional status. Methods: A quasi-experimental design was conducted in two-groups (control and intervention schools) on 453 students attending grade levels 4-5 in Bangkok. Two schools were selected for control, and two schools for intervention groups. The interventions included education, diet, physical activity (PA), food-environment, school builtenvironment, and life-skills components. Subjects were measured at baseline and at 6 months post-treatment. Results: The intervention group had significant differences in overall healthy practices (+1.5 mean difference, p=0.048), dietary habits, physical activity, lower total cholesterol (TC) levels (-2.43 mean, p=0.019) and higher high density lipoprotein cholesterol (HDL-C) levels (+4.06 p=0.028) as compared to the control. A higher reduction of overweight individuals among the intervention group over the intervention period was observed. Physical activity and consumption of vegetables increased while consumption of high-caloric snacks and fast foods decreased in children after the intervention. Conclusion: This study indicated that a multidisciplinary approach in school-based interventions is most likely to be effective in preventing children from becoming overweight in the long term. More research should be conducted on school-based interventions with longer intervention periods and higher sustainability.