This study empirically examined the effect of defense expenditure (DEXP) and internal security expenditure (ISEXP) on economic growth (proxy by GDP) in Nigeria during the period 1981 – 2018. Time series data such as DEXP, ISEXP and Gross Domestic Product (GDP) were obtained from Central Bank of Nigeria (CBN) Statistical Bulletin. Unit root test, Cointegration test and Error Correction Model (ECM) techniques were used to estimate the model while granger causality test was used to check the causal relationship of the variables. The results of the finding revealed that DEXP exerts positive and significant effect on GDP while ISEXP has a negative and insignificant effect on GDP. The results further revealed that there was evidence of unidirectional causality running from GDP to DEXP as well as ISEXP to GDP. Based on these findings, the researchers recommend that federal government should investigate any misappropriation of funds, proper monitoring of the activities of security agencies and overall administration of security architects in the system so as to achieve macroeconomic objective of sustainable economic growth in Nigeria