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Background and Objective: Childhood obesity is a significant public health concern due to its impacts on childhood physical and psychological health with subsequent adulthood complication. The aim of this study was to determine some related factors of obesity and overweight in girls' secondary school. Materials and Methods: This cross-sectional study was performed in Gorgan Northern Iran, during 2005-06. The subjects selected by stratified random sampling. Age, height, weight, BMI, daily time of television watching, frequency of physical activity and snack consumption was recorded by parents in a questionnaire sheet during a week. Data were analyzed by using SPSS-11.5 software, chi-square and ANOVA tests. Results: In this study, 6.3% and 41.7% of subjects were obese and overweight, respectively. The mean of BMI of girls was 19.69±4.6 kg/m2. The prevalence of obesity and overweight in Fars ethnic group was more than others (P<0.05). Average spending time for television watching was 2.35±0.98 hours and the same index was higher among the obese and overweight girls but, this difference was not significant. Food consumption during watching television, frequency and duration of physical activity were significantly related with obesity and overweight (P<0.05). Conclusion: This study showed that low physical activity and imbalanced nutritional behavior are related to obesity and overweight among secondary school girls in Gorgan-Northern Iran.