Objectives: Child undernutrition is a persistent public health problem contributing to about half of under-five child death in low-income countries, and it is severe among the poorest communities. The extent of socio-economic-related inequity in undernutrition within and between countries of different economic standing is still a question. This paper, therefore, aimed to examine the wealth-based inequity in nutritional status among 24 low, lower-middle, and upper-middle-income countries. Methods: The most recent demographic and health survey data of children under five years got included. Inequity in child undernutrition measured by concentration index (C) values; and concentration curves. Subgroup analysis by place of residence; and sex of the child was done. We then fit bootstrapped Mata regression to check whether there is a variation in inequality of child undernutrition across different income category countries.  Results: The overall prevalence of child undernutrition was 35%. The figure was highest in India (47%); and Ethiopia (38.9%), while it was lowest in Turkey (8.5%). Wealth-related inequalities in child undernutrition got detected in about half of the countries and all three economic categories. Child undernutrition was highly abundant among the poor households of Turkey [C:-0.26, 95% CI, -0.31 to -0.20]; and Cameroon [C:-0.19, 95% CI, -0.22 to -0.17], and relatively it was less concentrated among the poor in Liberia [C: -0.07, 95% CI -0.11 to -0.04], and Gambia [C:-0.07, 95% CI -0.11 to -0.04]. Meta-regression analysis revealed no difference in the inequality levels between the three economic categories of countries. Conclusions: The socio-economic-related inequality in child undernutrition within many of the included countries is still very significant. However, the economical category of countries made no difference in explaining socio-economic-related inequality in child undernutrition. Inter-sectoral collaboration to fight poverty and render special attention to the disadvantaged population segments would potentially help to address the observed inequity.