The present study investigated polyporoid mushrooms (Aphyllophorales sensu lato) commonly occurring in Poland-Daedaleopsis confragosa, Fomitopsis pinicola, Gloeophyllum sepiarium, Laetiporus sulphureus, and Piptoporus betulinus-for their content of phenolic compounds, including phenolic acids, in extracts of their fruiting bodies, and their biological activities. The contents of protocatechuic acid, p-hydroxybenzoic acid, and vanillic acid were determined by HPLC. Protocatechuic acid was the dominant phenol acid, with levels ranging from 17.7 μg to 90.0 μg/g dry weight. The highest total concentration of phenolic acids was observed in Fomitopsis pinicola (114.9 μg/g dry weight). The total content of phenolics compounds ranged from 6.80 to 21.88 mg/g dry weight. Fomitopsis pinicola and Gloeophyllum sepiarium contained the highest amounts of phenolic compounds (21.88 mg/g dry weight and 19.88 mg/g, respectively) and the highest antioxidant activity evaluated by FRAP method (55.79 and 87.82 mmol Trolox/kg dry weight, respectively).