Degree of poly (lactic acid) (PLA) foil degradation by the filamentous fungi i.e. Aspergillus ustus, A. sydowii, A. fumigatus, Paecilomyces lilicanus and Penicillium verrucosum has been investigated. A degradation process has been conducted in dynamic conditions at 30°C for 10 days in a medium containing 0.1% of foil as carbon source. To activate the enzymes involved in the poly (lactic acid) foil degradation, triple passaging on the medium has been conducted. Each passage lasted 10 days. After passages, increase of the mycelium biomass, its enzymatic activity and structural foil changes have been investigated using scanning electron microscopy (SEM) and differential scanning calorimetry (DSC). Strain passaging has resulted in the activation of the enzymes of the esterase group responsible for foil degradation, expressing itself in the mycelium biomass increase. Penicillium verrucosum and Aspergillus ustus appeared to be the most active strains. Structural and thermal changes of the material have been demonstrated. Filamentous fungi have a wide range of enzymes of the esterase group which, following initial activation, may actively participate in PLA foil degradation.