The kinetics of the thermal decomposition of MgCO3 was investigated using isothermal experiments performed in a thermogravimetric analyzer under a nitrogen atmosphere at 380, 400, 450 and 480C. The weight loss data as a function of time were modified to give the fraction that reacted () and the rate of reaction (d/dt) vs. time (t). Kinetic analysis of the experimental results, using three different methods, showed that diffusion predominates the MgCO3 decomposition over the investigated temperature range, with the data being best fitted by Jander's equation ([1(1)1/3]2=kt). The activation energy was estimated by Arrhenius plots using both the initial reaction rates and rate constants from fitting the above equation. The values estimated were 27.1 and 171.4 kJ/mol respectively.