The effect of mechanical milling on the thermal behavior of pyrophyllite ore from a deposit in Parsovici, Bosnia and Herzegovina, was characterized by X-ray powder diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, and Particle size distribution. The thermal behavior of the material was followed by thermogravimetric and differential thermal analysis and correlated to its microstructural properties. The Williamson-Hall model was used to calculate the crystallite size and microstrain. Mechanochemical treatment of pyrophyllite ore produced a substantial structural modification, mainly along the c axis, resulting in disorder and partial degradation of the crystal structure of the ore. The particle size diminution, induced defects, and microstrain in the crystal lattice cause decrease in the peak intensity until the final disappearance. As confirmed by scanning electron microscopy and particle-size-distribution analysis, the surface area and the agglomeration is more pronounced as grinding time increases. Dehydroxylation of the minerals in the unmilled ore was realized at 716oC confirm by FTIR analysis. The endothermic peak that corresponds to dehydroxylation is shifted toward lower temperatures and becomes broad giving rise to the formation of amorphous SiO2 as milling time increases.