Abstract: This study investigates the effects of monetary and fiscal policies on the real output growth in a small open economy. It is a country-specific, time series study that verifies the implication of increasing economic openness on the efficacy of monetary and fiscal policy. A modified GARCH model was used to estimate the anticipated and unanticipated shocks. Two measures of fiscal and monetary shocks were combined with openness and real oil price shocks in a VECM model to assess the effects of anticipated and unanticipated policy shocks on the output equations. The empirical results showed that anticipated and unanticipated fiscal and monetary shocks had no significant positive effects on real output. This suggests that the open macroeconomic version of the policy ineffectiveness proposition was valid for both monetary and fiscal policy shocks in Nigeria. This is in consonance with earlier works in this area. Furthermore, the degree of openness and oil price shocks had a negative implication on the efficacy of macroeconomic policy in Nigeria; also in agreement with the Dutch Disease Syndrome. Finally, the policy implication of this study therefore is that trade liberalization policy should be implemented cautiously. The Nigerian economy is weak to withstand the unwholesome consequences of full economic integration.