Overnutrition (overweight and obesity) is becoming increasingly more prevalent in children and adolescents with attendant grim consequences. Various tools are available for the identification of overnutrition but not all are simple and cost effective. It is therefore imperative to assess children and adolescents with a simple, easy, cheap and at the same time accurate and quickly implemented method for determination of overnutrition to facilitate prompt intervention and prevention of long term adverse effects of overnutrition. The study aimed at comparing mid upper arm circumference with BMI and BIA for determination of overnutrition in children aged 6-18 years in Egor Local Government Area of Edo State. It was a cross-sectional study conducted over a three-month period (October to December 2017). The study population consisted of 1,067 randomly selected children aged 6 to 18 years from public and private junior and senior primary and secondary schools in Egor Local Government Area of Edo State. The anthropometric measurements used include weight, height, body mass index and body fat derived from Bioelectrical Impedance Analysis. The overall prevalence of overnutrition was 17.6% for females and 9.3% for males respectively with the use of BMI, (p = 0.00) and 16.3% for females and 8.6% for males (p = 0.00) with the use of MUAC. However with the use of BIA the prevalence were 13.2% for females and 11.5% for males (p = 0.39) respectively. Irrespective of the method used, female subjects had higher prevalence of overnutrition than their male counterparts. The prevalence of overweight and obesity by BMI, MUAC and BIA, the gold standard was 9.6%, 3.8%, 6.0%, 6.4% and 5.4%, 6.9% respectively. Using percentage body fat by BIA in the determination of overnutrition as a gold standard, it was seen that both BMI and MUAC tended to overestimate overweight (9.6% for BMI, 6.0% for MUAC vs 5.4% for BIA) and underestimate obesity (3.8% for BMI, 6.4% for MUAC vs 6.9% for BIA). BMI overestimated overweight and underestimated obesity to a larger extent than MUAC. This can be explained by the fact that the BMI references and charts may lack generalizability and may not be applicable in some settings in developing countries such as Nigeria as the data for BMI charts was gotten from Western subjects. The ability of MUAC to estimate overnutrition correctly with AUC results from the ROC curve was generally good. The AUC for MUAC, was statistically significant in both genders in most ages. In general, sensitivity was relatively high for the cut-points chosen for all ages. The MUAC cutoff values for elevated percentage body fat were calculated to be approximately 18.75-31.5 cm in boys and girls. MUAC showed a strong positive correlation with fat mass, and even after correction for stature i.e fat mass index in females (0.866, 0.791, p < 0.000). The correlation between MUAC and fat mass and fat mass index was weaker in males (0.667 and 0.437 respectively, p<0.000). BMI showed a stronger positive correlation with fat mass, and fat mass index especially in females (0.917, 0.907, p < 0.000) than MUAC (0.866, 0.791, p < 0.000). Therefore, MUAC is a simple, easy, cheap and at the same time accurate and quickly implemented method for determination of overnutrition and can be used in addition to BMI for prompt and early diagnosis in children. This will in turn enhance prompt intervention and result in prevention of long term adverse effects of overnutrition.