By using magnesium carbonate tri-hydrates (MgCO3.3H(2)O) as starting material, anhydrous magnesium carbonate (MgCO3) was successfully synthesized by dehydration method under high pressure for the first time. The property of as-synthesized sample was investigated by powder X-ray diffraction (XRD) and Raman spectroscopy, respectively. The high pressure synthesis was performed at the various conditions to ensure that the optimal condition is 3 GPa and 800 degrees C for 1 h, and it is reasonable to explain the principle of MgCO3 synthesis under high pressure. The size of micro-particles observed from Scanning Electron Microscope (SEM) image exceeds to 100 mu m. As a good and important flame retardant material, its thermal property is investigated by Thermogravimetric (TG) analysis, Differential Scanning Calorimeter (DSC) measurement and high temperature X-ray diffraction (XRD) refinement, and the endothermic heat (128.59 KJ/mol), the thermal expansion coefficient along c-axis (alpha c = 1.639 x 10(-5)/degrees C), the thermal expansion coefficient along the a-axis (alpha a = 4.632 x 10(-6)/degrees C) and the volume thermal expansion coefficient (alpha v = 2.576 x 10(-5)/degrees C) was quantified. (C) 2017 Elsevier B.V. All rights reserved.