Aim: The objective is to find the prevalence of obesity among school children aged 6 to 12 years in Madurai and to investigate the factors promoting rise of weight in children. Methodology: It is a cross sectional observational study. The sample size is 2519 children from 2 rural and 2 urban schools. Height is measured by stadiometer and weight by electronic weighing machine. Body Mass Index is calculated and plotted on the Indian Academy of Pediatrics Body Mass Index chart (IAP-BMI) 2015 for boys and girls. Children are classified as underweight, normal, overweight and obese. Factors causing obesity assessed were age, gender, place of residence, birth weight, preterm/term, socio-economic status, Parents BMI, Environmental factors (physical activity, TV/Video gaming duration, Transport to school, Environmental safety), Food habits and sleep pattern. Result: The prevalence of obesity and overweight are 9.3% and 16.8% respectively. Obesity has strong association with the place of residence and socio-economic status (p__ampersandsignlt;0.001). No correlation was noted between age and gender in relation to obesity, but there is an increase in Mean and Standard deviation of BMI as the age increases. Regression analysis identified sedentary lifestyle; unhealthy food patterns like snacking, sleep deprivation and birth weight as risk factors. Protective factors identified were to prefer fruits and vegetables for healthy diet, adequate physical activity like walking to school, outdoor play etc. and visiting restaurants rarely. Parental obesity showed no correlation to the prevalence of obesity in their children. Conclusion: Prevalence of obesity among school children is 9.3% and overweight is 16.8% in Madurai. Modifiable factors are the commonest causative factor; hence early life style modification is of utmost importance to the native community.