A differential fixed-bed reactor was employed to study the reaction between Ca(OH)(2)/fly ash sorbent and SO2 under the conditions similar to those in the bag filters of the spray-drying flue gas desulfurization system. The Ca(OH)(2)/fly ash sorbent was prepared at weight ratio of 70/30, slurrying time of 16 h, and slurrying temperature of 65degreesC. Foil-like calcium silicate hydrates were found in the sorbent. The Ca(OH)(2)/fly ash sorbent was highly reactive towards SO2 and its initial reaction rate and maximum conversion were much higher than pure Ca(OH)(2). Increasing the relative humidity of the gas significantly increased the initial reaction rate and the maximum Ca utilization of the sorbent. Temperature and SO2 concentration had slight effects on the initial reaction rate and negligible effects on the maximum conversion. The reaction kinetics of Ca(OH)(2)/fly ash sorbent with SO2 was well described by the surface coverage model which assumes the sulfation rate being controlled by chemical reaction on sorbent grain surface and takes into account the surface coverage by products. The results of this study are useful to the design and operation of the dry or semidry processes using Ca(OH)(2)/fly ash sorbent to remove SO2 from flue gas.