Although biomass for biopolymer production is readily available today, biopolymers are still expensive to produce, which limits production. Biopolymers are increasingly used to reduce the negative impact on the environment. Polylactide is one of the most commonly used biopolymers. The properties of polymer materials can be improved by adding fillers, resulting in a polymer composite. In this work, the influence of different proportions of ZnO nanoparticles in composites based on biodegradable polylactide was investigated. The samples were prepared in a Brabender Kneader, then compacted in a hydraulic press and characterized using different techniques. The mechanical and thermal properties of the composites prepared were studied, and a goniometer was used to estimate the contact angle required to calculate the surface energy of the composites. The mechanical and thermal properties of the specimens were evaluated, and the mechanical properties of the specimens were studied using tensile tests on a mechanical testing machine. Differential scanning calorimetry was used to identify phase transitions, and the change in thermal stability was determined by thermogravimetric analysis of the material. The phase transitions were determined by differential scanning calorimetry, and the analyses performed showed that the addition of nanofillers affects the properties of pure polylactide. The results of contact angle measurements indicate a hydrophobic surface of PLA and a hydrophilic surface of ZnO. Mechanical tests showed that the properties of the polymer matrix can be affected by the addition of fillers and that the prepared composites have a brittle fracture. DSC analysis showed that the filler affects the glass transition temperature of the composite as well as the cold crystallization temperature. The TGA analysis confirmed that with a change in the filler content, the material properties also change.