This paper presents an analysis of CO2 mitigation potential in the transport sector between Lao PDR and Thailand. The Long-rang Energy Alternative Planning (LEAP) model was used to forecast transport service demand, energy consumption and CO2 emission of two selected countries during the period from 2010-2050. In this study, a stock vehicle turnover model was developed to assess the potentials of energy saving and CO2 mitigation of policies relevant to the transport sector in Lao PDR and Thailand. For this analysis, three mitigation actions were selected, namely, 1) fuel switching, 2) advanced technology and 3) modal shift to reduce energy consumption and CO2 emissions. Results of analyses show that, in the business as usual (BAU) scenario during 2010 to 2050 for Laos, it can save 9.4% of total energy consumption in 2050 while the cumulative CO2 emissions will be reduced by 15% in 2050. For Thailand, the energy consumption in the transport sector will increase by approximately two folds. However, in CO2 countermeasure scenario, the cumulative energy savings in 2050 will be approximately 5.2% while the cumulative CO2 mitigation in 2050 will be about 14.6% when compared to the BAU scenario.