Objectives: Estimation of the prevalence of underweight in the Bengali and Indigenous communities of under five children in the Chittagong Hill Tracts in Bangladesh and attempt to find its causal relation with feeding practice and household food security. Methodology: Descriptive QUANqual type of Crosssectional Comparison study. Collected data on 432 under five children and their families, half from Indigenous and remaining half from the Settler Bengali communities were analysed and compared to meet the objectives of the study. Results: No significant differences (p>0.5)were found in terms of prevalence of underweight in both communities. Direct and statistically significant association was found between mothers weight, duration of exclusive breast feeding and the nutritional status of the children only in the Indigenous group (P <0.05). No significant differences were found in terms of the household food secuirty and their contribution to nutritional status as a determinant. Begali children suffered comparatively more from fever (infectious diseasese) than that of the other group.