Non-isothermal decomposition kinetics of surface coated calcium carbonate (CaCO3) was investigated using different wt.% of nano-silica. The activation energy was calculated from model-free isoconversional technique using Kissinger-Akahira-Sunose method. The result indicates that CaCO3 with lower wt.% (0.25% and 1.0%) of nano-silica has low activation energy than pure and 2% nano-silica coated CaCO3. This is possibly because nano-silica acts as heat receptor and creates defects inside the crystal which is dominant at lower percentage of coating. However, higher % of nano-silica coating increases resistance to CO2 diffusion which increases the activation energy. The corresponding reaction model for decomposition was predicted by Malek's method. Experimental data was in good agreement with the theoretical model proposed by Sestak Breggren (SB). The parameters (m and n) in SB model and invariance of activation energy in the entire conversion range strongly signify that decomposition mechanism is single step in nature. (C) 2015 Elsevier B.V. All rights reserved.