Laboratory experiments were conducted to investigate the reactivity of partially sulfated limefly ash sorbents activated by water or steam for SO2 removal. Sulfation tests were performed at 550 degrees C using a fixed bed reactor under conditions simulating economizer zone injection flue gas desulfurization. Activation experiments were conducted with water or steam using a range of temperatures between 100 and 550 degrees C. The results showed that the reactivity of the sorbents was closely related to the content of Ca(OH)(2) formed in the activation process, which varied with the water or steam temperature. The sulfur dioxide capture capacity of Ca(OH)(2) in the sorbent is higher than that of CaO at a medium temperature. Water or steam temperatures in the range of 100-200 degrees C are favorable to the formation of Ca(OH)(2) from CaO.