The Kyoto Protocol is one of the most important international climate change treaties aimed at fighting global warming. On January 1st 2005, the protocol was enforced with its first commitment period 2008-2012. However, the effectiveness of reducing CO2 emission has long been debated. The purpose of this thesis is to empirically as-sess the impact of the Kyoto Protocol on carbon dioxide reduction across countries, whether the protocol led significant difference after entering force in 2005. The data used in this thesis cover 37 Annex B countries and 148 non-annex B countries from 1990 to 2007. The models are constructed on the basis of the various contributing fac-tors to CO2 emissions and the Environmental Kuznets Curve model. The main find-ing is contrary against the result expected. The insignificant dummy variable cannot indicate that there is a “structural break” of CO2 emissions reduction after the Kyoto Protocol was implemented. The conclusion is that political agreements such as Kyoto Protocol cannot show critical effects on reducing carbon dioxide. The underlying main driving factors of CO2 emission are energy use, electricity from coal source, fossil fuel burning, in other words, industrialization. And the technology develop-ments cannot keep in pace with finding a new energy source and effectively control-ling CO2 emissions in the short run.