Government spending on social sectors is an important tool for improving social capital and strengthening sustainable development. In Nigeria, public spending on education and health are expected to increase human capital, boost productivity and support long-term social and economic development. Despite the government’s spending in these sectors, there are still doubts about the effectiveness of such spending in achieving the desired social outcomes. The study therefore examines government expenditure on social investment in Nigeria, focusing on education and health financing from 2000 to 2025. The study was motivated due to the continuous concern on the sufficiency of government spending on human capital development. Time series data sourced from the Central Bank of Nigeria and the World Bank Data Indicators were used for the study. The data were estimated using the Autoregressive Distributed Lag (ARDL) model to ascertain the long run relationship among the variables after establishing their stationarity. The findings revealed that government expenditures on education showed a negative but statistically significant impact on social investment, while expenditures on health had a positive and statistically significant impact on social investment during the period of the study. Based on these findings, the study concluded that extra funding and good management of the education and healthcare funds are really important for improving social investment in Nigeria. The study recommends that policymakers should increase funding into the health sector and also make education spending more efficient, transparent, and properly monitored so that public resources could translate into better social and human outcomes.