The study examined how public health spending affects Nigeria's under-five mortality rate between 1988 and 2023 using time series data obtained from the CBN statistical Bulletin and World Development Indicators (WDI). Four explanatory variables were used in the study: the rate of female literacy, technology, HIV prevalence, and public health spending. After conducting unit root and co-integration tests, which showed a mixed order of integration among the variables, the Auto-regressive Distributed Lagged (ARDL) model was employed for the analysis. From the short run results, it was evident that Public Health Expenditure (PHE) has a positive and significant impact on under-five mortality rate, while HIV Prevalence Rate (HIVPR) and Technology (TCH) have a negative and significant impact on under-five mortality rate. In contrast, the long-run ARDL results indicated that, (PHE) has negative and statistically significant impact on under five mortality rate. Furthermore, HIVPR and TECH has a long-run positive and statistically significant relationship with under five mortality rate in Nigeria. Based on these findings, the study recommend that, to continuously reduce the under-five mortality rate in Nigeria, the government through the Ministry of Finance and Ministry of Health should improve budgetary allocation to the health sector at level at levels with adequate supervision to prevent wastage and misappropriation of funds. With these measures in place, Nigeria is believed to be on the right path toward achieving Sustainable Development Goal (SDG 3).