Background: With the rapid development of social and economic level, the rapid improvement of family economic income and the continuous transformation of social life style, the body mass index of adolescents and children has risen rapidly, the overweight and obesity rate has been significantly increased in social life, and it is now widely regarded as a serious global public health problem. Objectives:This present aimed to identify prevalence of Factors associated with Overweight and Obesity among 12-15 year old adolescents and children in Longnan City, Gansu Province" Methods:Nine schools in LongNan City were selected by questionnaire survey, and each school selected a class of students as survey objects to investigate the influencing factors such as height, weight, diet, exercise and family. Simple logistic regression model, multiple logistic regression model and backward elimination indicated were used for analysis. Results: A total of 620 adolescents and children were investigated in this study. Simple logistic regression model showed that gender, the number of fast food consumption per week, the number of chocolate consumption per week, the number of fruit consumption per week, the length of exercise per week, the number of exercises per week, the living area and family genetic history were correlated with the occurrence of obesity. Multiple logistic regression model and reverse elimination results showed that the risk of obesity was higher in males (OR=3.47) than in females. Statistically, eating fast food (OR=1.65), chocolate (OR=2.07), not participating in weekly exercise (OR=1.58), lack of weekly exercise time (OR=2.75), and not eating fruit (OR=1.53) were significantly associated with childhood obesity. We also found that children living in cities (OR=1.80) were more likely to be obese than those living in rural areas, and that children with a family genetic history of obesity (OR=2.20) were also at risk of developing obesity. Conclusion:In LongNan City, boys are more prone to obesity than girls. Eating behavior, number of exercises, length of exercise, area of residence and family genetic history are the main influencing factors for overweight and obesity in adolescents and children. Keywords: Adolescent Overweight,Childhood,Obesity.