Modified calcium hydroxide by propionic acid (MCP) Modified calcium hydroxide and magnesium oxide by propionic acid (MCMP) Thermogravimetric Model free approach Activation energy Reaction order Decomposition characteristics of the products of the modified calcium hydroxide by propionic acid (named as MCP) and the modified calcium hydroxide and magnesium oxide by propionic acid (named as MCMP) have been investigated through the thermogravimetric analysis. Thermal decomposition process of MCP and MCMP mainly consists of two mass loss segments which are the release of organic radical in low temperature zone and carbon dioxide in high temperature zone, respectively. As temperature heating rate is increased from 10 K min -1 to 17.5 K min -1 , the decomposition process is shifted to higher temperature zone, but not distinctly. However, the maximum mass loss rate is obviously increased at the higher temperature heating rate. Model free approaches of the Ozawa-Flynn-Wall method and the Vyazovkin method are used to calculate the activation energy and Avrami theory is used to estimate the reaction order. Variations of these two parameters at different reaction degrees demonstrate the multistage and complicated characteristics of MCP and MCMP during the thermal decomposition process.