Problem: There have been increase in the volume of Official Development Assistance (ODA) to developing regions of the world, especially Sub-Saharan Africa following the millennium declaration. Nigeria is the third highest receiver of ODA after Tanzania and Mozambique. Substantial part of these in-flows go to the health sector due to its importance. In addition, Nigerian governments’ allocation to the health sector has been increasing in recent years. Meanwhile the nature of the effects of spending these massive resources on the healthcare sector is not clear as there have not been concordance in the results of most past works. The study therefore examined the effects government health expenditure and health specific aid on infant mortality rate in Nigeria. Approach: Data on different variables for the study were from 1980 to 2021 sourced from World Development Indicator, Organization for Economic Cooperation and Development (OECD) and Food and Agriculture Organization (FAO) database. The data were analysed within the ARDL framework where short-run model, long run model and post estimation analyses were carried out   Findings: The bound test results indicated the presence of long run cointegration. The short run model results indicated that health aid did not have direct effect on under-5 mortality rate (U5MR) in Nigeria. Meanwhile, lagged under five mortality (U5MR), government expenditure on health (GEXH) (P<0.5) and its interaction with foreign aid for health (P<0.05), and GDP per capita (P<0.5) significantly reduced U5MR in the short run while GHEX (P<0.01) directly affected U5M outcome in the long run. It addition, GHEX’s interaction with foreign aid (P<05)reduce UMR significantly in the long run and the results suggested that the two variables were complement. Conclusion: The study concluded that health sector aid did not have any direct effect on U5MR while GHEX and its interaction with health sector aid improved U5MR and it was concluded that GHEX and AID were complementary. This study recommended improved government expenditure in the health sector while coordination and utilization of foreign aid for the health sector are specially monitored and guided in order to stimulate its effectiveness in reducing under-five mortality in Nigeria.