Reactivities of two sorbents, a limestone and a half calcined dolomite, with H2S under simulated pressurized coal gasification conditions were studied by using TGA techniques. Although the activation energies for both sorbents are found to be about 180 kJ . mol(-1), the initial reaction rate of the half-calcined dolomite (50 mu m) is about 30 times faster than that of the limestone (50 mu m). The reactions of both materials are first order with respect to HIS partial pressure. The pressure of CO2 and H2O has almost no effect on the sulfidation reaction of the half calcined dolomite, but has adverse effects on the reaction of the Limestone. Although, in general, the smaller particles ran react faster, it is found that the effect of particle size on the reaction rate is different, with d(p)(-0.17) for the half calcined dolomite and d(p)(-0.85) for the limestone.