CaCO3 is one of abundant minerals in nature, which is a promising material in thermochemical energy storage (TCES). In this work, we have succeeded in synthesizing CaCO3/ZrO2 composites by physical mixing with a magnetic stirrer using CaCO3 from natural limestone. The mixing was carried out by mechanical stirring with various molar percentages of CaCO3:ZrO2 of 100:0, 85:15, 70:30 and 50:50. The phase and structure of the CaCO3/ZrO2 composites were characterized by x-ray diffraction (XRD). Thermal properties were characterized by thermogravimetri analyzer. Morphology of the composites was observed by scanning Electron microscopy (SEM) with energy dispersive x-ray (EDX). Based on the XRD results, the peak intensity of CaCO3 at the crystalline plane of (104) decreased with increasing percentage of ZrO2. The lattice volume of CaCO3 also relatively decreases with increasing percentage of ZrO2. The increase in the percentage of ZrO2 in the CaCO3/ZrO2 composites makes the decomposition temperature also decreases. This is probably due to heat and mass transfer of ZrO2.