The increase of greenhouse gases (GHG) emissions is of major environmental problems. 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. We choose a model in which CO2 emissions are related to economic growth, trade openness, capital stock, labor force, and the energy consumption of Iran for the period of 1971-2005. The approach of generalized method of moments (GMM) is used for analyzing the variables’ relationships. The results indicate that economic growth has a negative effect on the CO2 emissions. And, the trade openness has significant positive impact on the CO2 emissions.