Literature on mother’s education and child health casually observes some nonlinearities and threshold in the relationship. Even though this nonlinearity or threshold has significant bearing on policy matters, any rigorous attempt to address this issue is missing in the literature. In this study we test the existence of such threshold using Demographic and Health Survey (DHS 2003) data for Nigeria. Large variations in the education policy and the public investment in education during 1950-1990 motivate the selection of the country and the construction of the instrument for endogenous mother’s education. With height for age z score (HAZ) as a proxy for long run child health capital, regression results reveal that there is hardly any significant effects of mother’s education on child health if mothers do not go past primary education. We use Hansen (2000) for threshold estimation and it also corroborates our hypothesis about the existence of a threshold. We argue that low cognitive ability through lower education, low quality of overall education, ineffective health education in curricula give rise to a fixed cost, and thus to the threshold in mother’s education-child health relationship.