Objective To study the overweight and obesity situation among Mongolian ethnic children and adolescents in the last 25 years and to provide a basis on related prevention and control measures.Methods A cross-sectional study was used,with 18 366 aged 7 to 18 Mongolian ethnic children and adolescents involved.Surveys on their physical health,in 1985,2000 and 2010 were carried out.Comparison on the mean of BMI and the prevalence rates of overweight and obesity in different years,genders,location of residence (urban or rural) was also made.Results Over the past 25 years,among the aged 7 to 18 Mongolian ethnic children and adolescents,the overall trend on their means of BMI was increasing.The prevalence rates of overweight and obesity in Mongolian ethnic children and adolescents were 2.1％,0.5％ in 1985,and 6.3％,2.4％ in 2000,with an increase of 2 to 4 times during the last 15 years.The prevalence rates of overweight and obesity were substantially increasing in the year 2010,to have reached 9.1％ and 6.6％,which were 4 to 12 times of the figures in 1985.The detection rates of overweight and obesity in urban boys were 1.2％,0 in 1985,7.9％,3.4％ in 2000 and 11.0％,11.8％ in 2010.However,the rate of obesity in the rural boys were 0.6％ and 0.6％ in 1985,2.8％,2.1％ in 2000 and 9.0％,3.4％ in 2010.In 1985 the rates of overweight and obesity in urban girls were 1.8％,0.3％,8.1％,4.3％ in 2000 and 9.4％,8.4％ in 2010.However,among the rural girls,the prevalence rates of overweight and obesity prevalence was 8.8％,2.2％ in 1985,4.5％,0.9％,in 2000 and 10.2％,4.5％ in 2010.The rates of overweight and obesity among groups in different years showed significant differences (P＜0.05).Conclusion Over the past 25 years,the prevalence rates on overweight and obesity increased significantly in Mongolian ethnic children and adolescents,and continued to rise,which called for reasonable and effective measures to be taken to prevent and control the occurrence of the problem.