Abstract: Objective To determine the prevalence of childhood overweight and its association with family socio-economic status (SES). Methods Data of children aged 7-18 years were extracted from the 1991-2009 China Health and Nutrition Survey. Childhood overweight was defined using criteria proposed by the China and International Obesity Task Force (IOTF). SES was measured with average household income per capita. The associations between SES and childhood body mass index (BMI) and overweight were analyzed by a multivariate linear regression model and a logistic regression model, respectively. Results A triple increase in household income and prevalence of childhood overweight was found during the period from 1991 to 2009. Increased household income was associated with increased childhood BMI. Children living in a low-income family were less likely to be overweight than those living in a high-income family 〔odds ratio (OR)=0.490, 95% confidence interval (CI): 0.266, 0.904〕. Conclusion Childhood overweight is associated with household income. Family intervention can help control childhood overweight problem in China.