Interfacial properties of the composite are provided on the basis of calculated values of the parameters of adhesion: the thermodynamic work of adhesion, interfacial free energy and the coefficient of spreading. Obtained values of adhesion parameters were correlated with mechanical and thermal properties of investigated nanocomposites. Interactions between polymer matrix and filler is a key factor in determining polymer composite properties. The aim of this thesis is the study of the interfacial, mechanical and thermal properties as well failure mechanisms of polycaprolactone and polylactide with the addition of untreated and methacryl silane pretreated alumina hydrate (ATH) filler. PCL/ATH and PLA/ATH composites with different volume fraction of untreated and methacryl silane pretreated ATH fillers were prepared by melt blending procedure. The effect of the filler addition on the PCL/ATH and PLA/ATH composite properties has been investigated using techniques of the contact angle, tensile testing, differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The failure mechanism and morphology of composites were studied using scanning electron microscopy. The properties of the interface of composites are estimated on the basis of calculated values of the parameters of adhesion; thermodynamic work of adhesion, interfacial free energy and spreading coefficient. The obtained values of the parameters of adhesion were connected with mechanical and thermal properties of composites investigated. A significant influence of modifications ATH fillers on the mechanical and thermal properties of the PCL/ATH and PLA/ATH composites, which can be attributed to stronger interactions at the interface polymer / filler with treated ATH filler.