Sulfur capture reactions of CaCO3-H2S and CaO-H2S have been investigated under various gaseous mixtures conditions using limestone and calcined limestone of 1 mm diameter in a thermogravimetric analyzer. Sulfidation of limestone (CaCO3-H2S) had a very low initial reaction rate and final conversion than the sulfidation of calcined limestone (CaO-H2S) due to its product layer having less porosity than those produced by calcined limestone. The products (CaS) produced by sulfidation of limestone have larger grain size and lower specific surface area than those produced by calcined limestone, Both sulfidation reactions of limestone and calcined limestone were first order with respect to H2S partial pressure. The presence of CO2 inhibited both the initial reaction rate and final conversion of sulfidation of calcined limestone. This was explained by the fact that CO2 accelerated sintering of CaO, and thus reduced the specific surface area of CaO. The initial sulfidation rate of limestone decreased linearly with increasing CO2 partial pressure, The initial reaction rates of both limestone and calcined limestone decreased with increasing steam partial pressure. The effect of steam on final conversion of sulfidation of calcined limestone was found to be insignificant. Only with the presence of CO2 was the sulfidation rate of calcined limestone appreciably reduced by H-2 addition.