A cross-sectional study investigating the prevalence of underweight and overweight in school-aged children from Rio Branco, Acre State, based on the 2007 WHO growth reference, was carried out. A total of 706 children between 8 and 14 years of age, enrolled in public primary schools at 3^rd and 4^th grades were assessed. For the assessment, the school children were stratified into age bands of 8 to 9 years, 10 to 11 years, and 12 to 14 years. The overall prevalence of overweight was 17.6% (17.3% boys and 17.8% girls) while prevalence of underweight was less than 3.0%, a level within normal limits for this population. The study results showed that overweight is becoming a major public health problem among children at state primary schools in urban areas of Rio Branco, Acre.