For the removal of acid gases it, flue gas from, municipal solid waste incineration, simultaneous Sorption Of HCl and SO2 in CaO fine particles was conducted ill the ternperature range 473-1073 K, in simulated gas atmospheres comprising mixtures of HCL SO2, N-2, H2O and CO2. The effect of H2O and CO2 on the sorption of HCl and SO2, on CaO was investigated. The maximum Capacity of HCl sorption oil CaO was found at 873 K in all gas mixtures employed. However the HCl sorption on CaO was considerably inhibited by the presence of SO2, H2O N-2, system. The reverse reaction of HCl emission from the reaction product, CaCl2, was considered responsible for a lower HCl sorption on CaO. On the other hand, the capacity of SO2 sorption on CaO was lower in the HCl-SO2-O-2-N-2 system than the SO2-O-2-N-2 system. At a higher temperature of 1073 K, the capacity of SO2 sorption on CaO became remarkably higher in the HCl-SO2-O-2-N-2 than the HCl-SO2-O-2-N-2 system, However, SO, sorption capacity was Further decreased by the presence of CO2 in the HCl-SO2-O-2-N-2-H2O-CO2 system, which might be caused by carbonation of CaO and CaCl2, with CO2.