The study set out to investigate the effect of external debt on Nigerian economy. Time series data for twenty-two years that span from 1994 to 2015 were obtained and subjected to test using Ordinary least square regression (OLS) for the hypotheses formulated for the study. The study revealed some forms of long run relationship between Gross domestic product, on the one part and external debt, external debt service and export, on the other part but of particular importance is the long run marginal negative relationship between external debt and Gross domestic product. The study further confirmed causality, from predictors to dependent variable and recommended that there should be a ban on external debt in Nigeria, for some time. However, where external debt is unavoidably necessary for productive venture/investment that can boost export, it should be for such specific venture/investment and should be well managed to pay back the external debt and its associated service cost, thereby justifying the decision for such external debt without further stress on the economy.