Emission factors of CO2, SO2 and NOx emitted from Iran's thermal power plants are fully covered in this paper. To start with, emission factors of flue gases were calculated for fifty thermal power plants with the total installed capacity of 34,863 MW over the period 2007-2008 with regard to the power plants' operation characteristics including generation capacity, fuel type and amount and the corresponding alterations, stack specifications, analysis of flue gases and physical details of combustion gases in terms of g kWh(-1). This factor was calculated as 620, 2.57 and 2.31 g kWh(-1) for CO2, SO2 and NOx respectively. Regarding these results, total emissions of CO2, SO2 and NOx were found to be 125.34, 0.552 and 0.465 Tg in turn. To achieve an accurate comparison, these values were compared with their alternatives in North American countries. According to this comparison, emission factor of flue gases emitted from Iran's thermal power plants will experience an intensive decline if renewable, hydroelectric and nuclear types of energy are more used, power plants' efficiency is increased and continuous emission monitoring systems and power plant pollution reduction systems are utilized. (C) 2010 Elsevier Ltd. All rights reserved.