The objective of this study is to explore the scenarios of energy-related greenhouse gas mitigation in Thailand to 2030. The picture with no change of government policy which is relied on the existing plan namely ‘reference scenario’ is simulated. Ambitious target of renewable energy deployment with the priority of energy supply security is adopted. Alternatively, a case with undergo progress of the committed plan namely ‘case without plan’ is also compared to reveal the impact of government policy uncertainty, particularly nuclear power and implementation of road-to-rail policy. This scenario will also present the pessimistic prospect on renewable energy development. On the other hand, a case with more concern on greenhouse gas emission reduction called ‘additional plan’ is comparatively conducted to evaluate the impact of additional non-existing policies on greenhouse gas mitigation. In this case, the proposed measures in the energy efficiency scheme with more nuclear power generation is considered to minimize the energy-related greenhouse gas in Thailand.