Background: Under nutrition is one of the most imperative problems among children that needed to be addressed in the realm of public health. Undernourished children cannot maintain natural biological abilities, such as growth, recuperating from ailments, learning and physical development. Poor feeding practices along with illnesses like diarrhoea, pneumonia, helminthic infections etc. are major determinants of under nutrition in India. The tribal populations in India are identified to be the autochthonous people of the land thereby being one of the major sufferers of under nutrition. This study aimed at finding out the prevalence of under nutrition among under-five children in tribal population in Tiruchirappalli district of Tamil Nadu.Methods: This community based cross-sectional analytical study was done among Malayali Tribes population of Puthur village, Pachamalai Hills, Trichy to determine the prevalence of under-nutrition using CIAF and WHO Z scoring system and its risk factors by multivariate analysis.Results: Out of 100 children, about 85% were undernourished as per CIAF criteria. In the Multivariate analysis, children of employed mother and children who were not given exclusive breast feeding were associated with Under nutrition which was statistically significant (p<0.05).Conclusions: CIAF could be considered as a better measure than any other single index to identify the problem in the community. The study also emphasizes the significance of proper IYCF practices among employed mothers and improvement of MCH services in Tribal population during antenatal and immediate postnatal period to bring down the prevalence of under nutrition.