The degradation behavior of a calcium hydroxide sorbent for SO(2) removal was investigated in terms of microstructure and crystal phase change. Hydrated lime sorbents with a high surface area were prepared by hydration of Diethylene glycol-coated quicklime. A durability test for sorbents was carried out in a consistent chamber condition at a temperature of 50 degrees C and a humidity level of 60% relative humidity for 168 h. With respect to SO(2) reactivity, the deteriorated sorbents showed lower reactivity toward SO(2) gas than an as-prepared sorbent. And the longer degradation time the hydrated lime sorbents were exposed to a humid atmosphere, the lower their SO(2) reactivity became because the specific surface area of sorbents decreased from 41.23 m(2)/g to 15.23 m(2)/g. The calcite crystals formed in the deteriorated sorbents due to carbonation and the calcite crystals were grown with the elapse of degradation time. Accordingly, the SO(2) removal efficiency of the deteriorated sorbents was lower than that of the as-prepared sorbent. It could be concluded that the degradation behavior of calcium hydroxide sorbents originated from the formation and growth of calcite in them. (C) 2010 Elsevier B.V. All rights reserved.