Background: Nutrition is a major determinant of a child’s overall development and learning. The new trend of malnutrition, described as double burden of malnutrition, is one in which under-nutrition is coexisting with over-nutrition and is a major problem facing the world today. Under-nutrition is the most common health disorder among children, linked with various diseases causing death in developing countries. There is paucity of data on the burden of under-nutrition among school aged children in Ilorin and Nigeria as this is presently not routinely done hence this study.Objective: To determine the prevalence of under-nutrition among school age children in Ilorin.Methods: A cross sectional descriptive studies of school aged children in Ilorin Kwara State using a multi – staged sampling techniques. Sixteen primary schools, eight public and equal number of private school pupils were recruited for the study. The anthropometric measurements were taken to determine the anthropometric indices using the World Health Organization (WHO) reference 2007.Results: A total number of 480 primary school pupils from Ilorin were recruited. Males were 221 (46.0%) with a M:F of 1:1.2 and a mean age of 9.2 ± 1.8 years. The prevalence of underweight and stunting were 15.4% and 11.5% respectively. There are more underweight and or stunted children among the public school pupils compared with the private school pupilsConclusion: The study brings to the fore the magnitude of under-nutrition among school children in Ilorin Nigeria. Routine nutritional assessment of primary school children is advocated as against the present practice where such an important survey is limited to once and at the point of school entry only. The ongoing pilot school meal programme should also be extended to all states of the federation