OBJECTIVE: To study the prevalence of obesity and the influencing factors for obesity in primary school students from Kaifu District of Changsha City. METHODS: A total of 4 140 students aged 7 to 12 years sampled randomly from Kaifu District of Changsha City were enrolled. Obesity was identified based on the body mass index (BMI). The influencing factors for obesity were investigated by non-logistic regression analysis. RESULTS: The prevalence of overweight and obesity were 9.76% and 7.39% respectively, and the prevalence of obesity in boys and girls were 9.37% and 5.13% respectively (P<0.05). The obese children had significantly higher BMI, waist circumference (WC), waist to hip ratio(WHR), percentage of body fat (%BF), systolic blood pressure, and serum triglyceride (TG) and low density lipoprotein-cholesterol (LDL-C) levels but significantly lower serum high density lipoproteincholesterol (HDL-C) level compared with the children with normal weight. BMI, %BF, WC and WHR were all positively correlated to serum levels of TG and LDL-C in obese children. Binge overeating, increased television viewing time, fast speed of eating and increased consumption of fried foods are all risk factors for the development of obesity. Preference for physical activity and sufficient physical activity were protective factors for obesity. CONCLUSIONS: The prevalence of obesity of primary school students from Kaifu District of Changsha City is high in China. The development of childhood obesity is associated with poor eating behaviors, less physical activity and increased television viewing time. The control of childhood obesity may be beneficial to early prevention of some adult chronic diseases.