<p><span style="font-size:11pt"><span style="font-family:Calibri,sans-serif">In this work, polymer composite materials based on polypropylene (PP) and layered silicates were obtained by melt mixing method. The research looked into the effect of the amount of compatibilizer on thermal and mechanical properties of composites based on two types of layered silicates with modifiers of different interlayer densities, with maleic anhydride grafted polypropylene (MA-p-PP), which was used as a compatibilizer. The compatibilizer was changed to 3, 6, 9 and 12 % while the amount of filler in the composite remained at 3 %. Cloisite15A, a layered silicate with a higher modifier density, produced intercalated structures, while Cloisite20A, with a relatively lower modifier density, produced mostly exfoliated nanocomposites. Forming of the nanostructure led to a significant increase in thermal stability (50 % weight loss was observed at temperatures of 360 and 430 °C for polypropylene and its based nano-composites, respectively). The analysis of the mechanical properties of nanocomposites showed that the elastic modulus increases by 15–20 %, and this effect is more expressive for exfoliated structures, however, the yield stress remains practically unchanged, and a significant decrease in elastic deformation is observed.</span></span></p>