A highly active macroporous sorbent for high-temperature desulfurization was prepared by swelling raw lime in a water-acetic acid mixture. The desulfurization capacity of the macroporous lime was compared with the raw lime, lime treated with liquid water, and lime treated with acetic acid vapor. It was found that the reactivity of the lime treated with water-acetic acid mixture depended on the content of calcium acetate in the precursor, a mixture of calcium acetate and calcium hydroxide. The desulfurization capacity of this sample reached the same level as the acetic acid vapor treated lime when the calcium acetate content of the precursor was 46.7%, but was much higher than the water-treated sample or the raw lime. The acetic acid-water swelling process is much more economical than the acetic acid vapor swelling method. Furthermore a mixture of water-acetic acid has a less offensive odor than pure acetic acid vapor. The higher reactivity of the lime prepared by acetic acid-water swelling method was due to the macropores (larger than 200 nm) produced during the swelling process. These macropores provide a diffusion route for SO2 in the sorbent during the sulfation and did not become plugged. It was concluded that a highly reactive and practical lime should possesses an adequate number of pores, adequate pore distribution, and good connection of the different size pores for good permeability of reactant gases and to prevent the plugging of the pores by sulfation.