[en] In this study, Mn-substituted siderites with different substitution amounts were prepared and characterized by using XRD (X-ray diffraction), TEM (transmission electron microscope), TG and DTG (thermogravimetry and derivative thermogravimetry) and Raman spectroscopy. The effect of Mn substitution on the crystal structure of siderite and thermal decomposition processes of synthetic siderite was investigated. The substitution of Mn for Fe in the crystal structure of siderite resulted in an increase in a and c dimensions from 4.702 and 15.374 to 4.718 and 15.43 Å as the substitution amount increased from 0 to 7.4%, respectively. The substitution of Mn also decreased the crystallinity of siderite. The thermal decomposition of synthetic siderite took place at approximately 350 °C. However, the substitution of Mn for Fe increased the decomposition temperature and improved the activation energy (E_d) values from 126.3, 155.7, 156.8 to 164.5, 167.6, 170.3 kJ mol⁻¹ when Mn substitution increased from 0 to 7.4 mol%.