In this paper, we examine the co-benefits of reducing CO2 emissions in Thailand during 2005-2050 in terms of local pollutant emissions as well as the role of renewable-, biomass- and nuclear-energy. It also examines the implications of CO2 emission reduction policy on energy security of the country. The analyses are based on a long term energy system model of Thailand using the MARKAL framework. The study shows that the power sector would account for the largest share (over 60%) in total CO2 emission reduction followed by the industrial and transport sectors. Under the CO2 emission reduction target of 30%, there would be a reduction in SO2 emission by 43% from the base case level. With the CO2 emission reduction target of 10-30%, the cumulative net energy imports in the country during 2005-2050 would be reduced in the range of over 16 thousand PJ to 26 thousand RI from the base case emission level. Under the CO2 emission reduction targets, the primary energy supply system would be diversified towards lower use of coal and higher use of natural gas, biomass and nuclear fuels. (C) 2010 Elsevier Ltd. All rights reserved.