The increase of greenhouse gases (GHG) in which CO2 emissions constitute the principal component, is of major environmental problems of all societies. Economic growth impels intensive use of resources and as a result, more residues and wastes thrown in the nature that could lead to environmental degradation. This article tries to trace the eventual relationship between trade openness and environmental degradation in Iran. For this purpose, a multivarate model is employed in which economic growth and trade openness are related to CO2 emissions for the period of 1971-2006. By carring out the Granger causality test, there appeared a unidirectional relation from trade openness to CO2 emissions. To analyze the variables’ relationships, the approach of GMM is applied. Results indicate that economic growth has a significant negative effect on carbon dioxcide emissions. But, the impact of trade openness on carbon dioxcide emissions is significantly positive.