Experiments on thermal decomposition of nano-sized calcium carbonate were carried out in a thermogravimetric analyzer under non-isothermal condition of different heating rates (5 to 20K.min(-1)). The Coats and Redfern's equation was used to determine the apparent. activation energy and the pre-exponential factors. The mechanism of thermal decomposition was evaluated using the master plots, Coats and Redfern's equation and the kinetic compensation law. It was found that the thermal decomposition property of nano-sized calcium carbonate was different from that of bulk calcite. Nano-sized calcium carbonate began to decompose at 640degreesC, which was 180degreesC lower than the reported value for calcite. The experimental results of kinetics were compatible with the mechanism of one-dimensional phase boundary movement. The apparent activation energy of nano-sized calcium carbonate was estimated to be 151 kJ.mol(-1) while the literature value for normal calcite was approximately 200 kJ.mol(-1). The order of magnitude of pre-exponential factors was estimated to be 10(9) s(-1).