Abstract: Objective To investigate the prevalence of overweight and obesity,the nutritional status of dietary calcium and the relationship between childhood obesity and calcium intake in school-age children of Shanghai city.Methods A cross-sectional study was conducted in school-age children of Shanghai city.Medical examination as well as food frequency questionnaire were adopted to collect information on calcium intake and obesity.Results The incidence of childhood obesity was 36.0%.The average calcium intake was 647mg/d and only 26.4% of subjects had calcium intake of reference nutrient intake(RNI).The increase of total calcium intake didn't significantly reduce the incidence of obesity(χ²=0.319,P=0.956).While the increase of calcium intake per unit weight significantly reduced the incidence of obesity(χ²=65.022,P=0.000).With the increase of calcium intake per unit weight,body weight(χ²=101.660,P=0.000),body mass index(χ²=85.223,P=0.000),percentage of body fat(χ²=64.869,P=0.000),systolic blood pressure(χ²=35.626,P=0.000),diastolic blood pressure(χ²=24.779,P=0.000)and other obesity related indexes decreased.Conclusion The increase of the calcium intake per unit weight reduces the incidence of obesity in school-age children.