This paper evaluates the economic and environmental impacts andimplications of the mid-term greenhouse gas(GHG) emissions reduction targetscenarios of Korea by utilizing a computable general equilibrium model. Itpoints that the contribution of Korea’s participation in the reduction scenariosto global GHG reduction is negligible, because its share in global GHGemissions is low. It also shows that the participation of big emitting countriessuch as China and India is one of the most important factors for theenvironmental effectiveness of the Post-Kyoto regime. It also finds that, toachieve the target scenarios, the real GDP of Korea will decrease by0.58%~1.47% relative to the level of business-as-usual in 2020, which ismuch higher than the level of Korean government’s estimation. The uncertaineconomic cost may lead the Korean economy to wrong direction. Therefore,the economic cost should be verified again based on systematic andcomprehensive approach and analysis.