The direct sulfation of limestone from different sources in Iran was studied in a thermogravimetric analyzer under atmospheric pressure. All limestone samples tested have higher than 97% CaCO3. Experimental conditions were as follows: particle size levels ranging from 1.6 mum. to 7.8 mum, four level reaction temperatures (700degreesC, 750degreesC, 800degreesC and 850degreesC), and two SO2 concentrations (2.4 x 10(-3) and 3.2 x 10(-3) mol(.)mol(-1)). The particle size and temperature showed dominant influences on the rate and level of conversion while the effect of SO2 concentration was weak. The shrinking core model can be used to describe the behavior of the sulfation process. The reaction kinetics and diffusion mechanism are both important in controlling the rate of the process. The two key parameters of the model, chemical rate constant K-S and effective diffusion coefficient D-eff were obtained. Model predictions are in good agreement with the experimental data.