This work investigates composites of biodegradable polylactide (PLA) reinforced with mineral fillers - Schwerspat (S) and Glimmer POS (GL). Composites with 0.1; 0.5; 1 and 5 weight % filler were prepared in a Brabender mixer and molded under pressure. Composites with 0.1 and 1 weight % Schwerspat and Glimmer were prepared by solution mixing and molded under pressure. The mechanical and thermal properties of the composites and pure polymer were investigated and compared to each other. An overview of the mechanical properties of PLA and prepared composites was achieved through experiments with an universla testing machine. The tensile strenght, Young's modulus and elongation of the materials were determined. Dynamic mechanical analysis was used to investigate the primary viscoelastic properties of the materials and the effect of fillers on the glass transition temperature of the polymer matrix. The thermal stability of the samples was monitored by thermogravimetric method and insights into phase transition temperature of the phase transition of the polymer (matrix) obtained by differential scanning calorimetry. The contact angles of test liquids (water, formamide and diiodomethane) and free surface energy were also determined. Characterization of the composite materials revealed that the addition of fillers to polylactide improves its properties. In the presence of fillers the polymer matrix needs more time for phase transitions which can be seen in the shift of glass transition, christalization and melting temperatures to higher values. DSC analysis also showed that by the addition of fillers the cristalinity of the polymer lowers. The filler increases the load carrying capacity of the polymer matrix, evident from the increase in storage modulus. Composite materials also have better mechanical properties, ie. higher Young's modulus, tensile and breaking strength as well as elongation. Composite materials are thermally more stable than the pure polymer. Thermal degradation starts at 50 °C higher temperature than the pure polylactide.