Objectives We sought to explore 25-year trends of gender disparity in the prevalence of obesity and overweight both in urban and rural areas among Chinese children from 1985 to 2010.

Methods Data included 1 280 239 children aged 7–18 years enrolled in the Chinese National Survey on Students's Constitution and Health (CNSSCH), which is the largest nationally representative sample of school-aged children in China. Obesity and overweight were defined according to both WHO and the International Obesity Task Force (IOTF) definitions. Logistic regression was used to estimate the prevalence OR (POR) of gender for obesity and overweight prevalence in different surveys.

Results The prevalence of obesity increased (WHO definition: from 0.10% to 4.3%; IOTF definition: from 0.03% to 2.2%) over the past 25 years in urban and rural areas among Chinese children and it was much higher among boys than girls at each survey point (p<0.01). The increasing trend was significant in all age subgroups (p<0.01). Although the prevalence of obesity continuously increased in boys and girls, the changing pace was more rapid in boys than in girls. PORs of boys versus girls for obesity also increased over time, and the estimates of PORs were higher in urban areas than in rural areas at each survey point.

Conclusions The gradually increasing gender disparity in urban and rural areas suggests that the prevalence of obesity and overweight in boys, and especially in urban boys, contributes to a large and growing proportion of obese and overweight children.