Isoconversional methods combined with thermogravimetry were applied to investigate the decompo-sition kinetics of bastnaesite concentrates with different amounts of calcium hydroxide added. The apparent activation energy was calculated, and the results indicate that the overall reaction involves more than one single step. The reaction with a lower content (15 wt％) involves another step which denotes the decomposition of newly formed calcium carbonate during roasting. The activation energy increases with increasing amount of calcium hydroxide in the lower range (0-15 wt％). This is due to the resistance of calcium hydroxide to heat and mass transport. However, more calcium can promote the decomposition reaction more effectively and thus reduce the activation energy. Nonlinear fitting was performed by fitting the experimental data to Avrami-Erofeev model to determine the reaction model and pre-exponential factor. The theoretical models were proven to be reliable for kinetic prediction.