Abstract: Objective To investigate the prevalence and risk factors of overweight and obesity among floating primary and middle school students in Beijing.Methods Totally 2461 floating primary and middle school students in Beijing were selected with multistage random cluster sampling for a questionnaire survey and physical examination in June 2010.Results The overall prevalence rate of overweight and obesity were 8.6%(9.9% for the males and 7.0% for the females) and 5.5%(6.9% for the males and 3.8% for the females) among the students, respectively.There were significant gender differences in the prevalence rate of oversight and obesity(P<0.05).The prevalence rates of overweight and obesity in the primary school students were 8.9% and 6.4% and those in the middle school students were 8.0% and 3.5%, respectively, with significant differences in the prevalence rates between the two groups(both P<0.05).Multinomial logistic regression analysis showed that using computer with online service and with familial history of overweight or obesity were related to overweight(both P<0.05);male gender, longer duration of migration, fewer children in the family, higher education background of mother, familial history of overweight or obesity, and less physical exercise were related to obesity(all P<0.05).Conclusion Overweight and obesity among floating primary and middle school students relate with many factors, including family characteristics, life style and genetic influence.