Body Mass Index (BMI) is a measure of adiposity and has been used in many countries for assessment of overweight and obesity. The prevalence of obesity in children is increasing and is recognized as risk indicator of cardiovascular disease in adulthood. The study aimed was to document the Body Mass Index of school children aged 4-10 years. The study also determined the prevalence of overweight and obesity. This is a descriptive study of obesity prevalence in Nigerian Children. The weight and heights of the sampled children were measured and their BMI was calculated as weight/height (m2). Overweight and obese children were identified using charts from pooled internationally accepted data age and sex specific cut -off points for BMI. The BMI ranged from 09.25kg/ m2.to28.20Kg/m2 with a mean BMI of 15.10 kg/m2. The mean BMI for males was 15.64 and the females 14.56. The prevalence of Underweight, Healthy weight, overweight, and obesity were 16.33%, 64.34%, 12% and 7.33% respectively. More males were significantly overweight than females. Prevalence of overweight and obesity were highest in the highest socioeconomic class. Most children had BMI within the normal range. The prevalence of overweight and obesity though predominantly low should be taken seriously, especially as it appears to be associated with improving socioeconomic status. School health education (physical activity and nutritional education) is recommended as preventive measures.