In view of the ambiguity concerning the effect of CO2 on the consumption Of desulfurizing agent and based oil our previous findings when Studying flue gas desulfurization (FGD) byproduct, a specific study on the influence of CO2 has been carried Out here with Ca(OH)(2) being employed as a desulfurizing agent. This study is based oil compositional analyses of the reaction products, and combined measurements have provided relatively precise compositions of the reaction products derived from Ca(OH)(2) and flue gases. It has been found that the presence of CO2 does have in effect oil the desulfurization reaction and oil the consumption of desulfurizing agent when Ca(OH)(2) is employed as the sorbent for SO2. Also, the formation of CaCO3 is inevitable at about 70 degrees C and is enhanced Under conditions of high humidity. Although over 90% SO2 removal efficiency Could be achieved with a relatively high Ca/S mole ratio, the effective utilization of desulfurizing agent Would be low because CaCO3 is not the targeted product. Therefore, in order to improve semidry FGD technology, measures Must be taken to prevent the reaction between CO2 and Ca(OH)(2) so as to increase the Utilization ratio of the desulfurizing agent.