Abstract: The thermal decomposition of three ultra-fine CaC03 having different particle sizes and agglom-eration states was investigated.The kinetic parameters obtained by using the contracting volume mecha-nism R3 and Coats and Redfern's equation were in good agreement with those using Kissinger non-mecha-nism equation. Furthermore，the result showed that a considerable diminution of the activation energy Ea up to 60~80 kJ·mol^-1 is observed in the case of ultra-fine calcite. The Voigt analysis of the X-ray diffrac-tion data for the samples showed that abnormally large strain existed in the lattice of these samples. We suggest that this may be the reason of their abnormal decomposition behavior. At the same time，we ob-served that the conglomeration states revealed by TEM and SEM images result in the minute difference be-tween those ultra-fine CaCO₃.

Key words: Ultra-fine CaCO₃, Non-isothermal decomposition kinetics, Lattice distortion