Light mineral fillers are natural inorganic materials of various compositions that have been used in a practical way since the beginning of the rubber industrial processing. Depending on the application, natural kaolin is often modified by physical processes or by chemical processes (pillaring, adsorption, intercalation, functionalization, acid activation, etc.). It is important to modify kaolin due to improve its properties to adsorb inorganic as well as organic molecules. In the introduced study, kaolin from Kaznějov deposit was modified by potassium acetate, dimethylsulphoxide and silane treatment. Different techniques such as thermal (DTA) and spectral (FTIR) were used to characterize modified kaolin samples. On images from a scanning electron microscope (SEM), we observed the incorporation of modified forms of kaolin into the matrix of the rubber mixture. The main aim of the study is to observe the influence of filler based upon modified kaolin forms on the physico-mechanical properties and structural changes of rubber mixtures. Modified kaolin was mixed into a rubber blend in particular ratio of 5, 10, 24 phr in combination with carbon black. The effect of modified kaolinite on the curing characteristics (M_L, M_H, t₉₀, Rv) and mechanical properties (TS_b, E_b hardness) in sulfur-cured rubber composites was investigated.