The article presents the results of investigations concerning the analysis of milling kinetics of chosen rock materials taking into consideration their strength properties. Investigations were carried out for a mill operating on a semi-industrial scale. Milling was conducted in a periodical mode using grinding media differing in diameters. Mineral raw materials differing in terms of crystallographic structure were subjected to grinding. The process of milling was carried out for quartzite, granite and greywacke. Input fraction of ground material was of size 5 – 8 mm. Grain strength from particular size fractions and its influence on the process kinetics were determined. Grinding rate of particular size fractions and basic parameters used in the theory of statistical moments were calculated.