In this study, the calcination reaction of 10 different limestone samples which were taken from different regions of Turkey was investigated by using thermogravimetric analysis (TGA) technique. Various models were applied to the experimental results and it was found that the shrinking core model with surface reaction rate controlling mechanism is the best model fitting the experimental data Application of this model to the experimental data showed that the calcination activation energies of various limestone samples char,ge in the range 40-50 kcal/gmol.