The capture of H2S or SO2 with Ca-based absorbents, limestone and dolomite, was investigated under a periodically changing condition between reducing and oxidizing atmospheres, taking account of the coexistence of these atmospheres in a fluidized-bed coal gasifier. The degree of desulfurization in the reducing atmosphere was large compared with that in the oxidizing atmosphere. Apparent difference in desulfurization behavior was scarcely observed between limestone and dolomite. Stabilization of CaS in in situ desulfurization residues derived from both limestone and dolomite to harmless CaSO4 was also investigated. Absorbents maintaining porous-structure, such as dolomite, will be preferable for desulfurization in the coal gasification/combustion types of hybrid power systems.