The crystal structural deformation of dolomite caused by intensive grinding was investigated by X-ray diffraction (XRD), thermal analysis. Applying high temperature XRD, attention was mainly directed to the change of the thermal decomposition of mechanically treated dolomite. Grinding experiments for 1, 5 and 7 h were carried out in FRITSCH pulverisette5/2 planetary mill. Structurally deformed dolomite crystallites developed due to the mechanical treatment decomposes in two steps at higher and lower CO2 partial pressure as well. Deformed dolomite decomposes directly to calcite and periclase accompanied by the formation of CO2 between 500 degrees C and 600 degrees C. The proportion of structurally distorted dolomite increases with the grinding time.