Laetiporus sulphureus (chicken of the woods) is a wood decaying mushroom with positive medicinal and biological effects. The aim of this study was to determine its chemical composition including the main organic components (protein, fat, fibre, and ash contents, different protein fractions, the free amino acid level, soluble oligo- and polysaccharides, phenolics), the in vitro digestibility, the free radical scavenging activity, and twenty mineral elements.Our data demonstrate the characteristic in general valuable chemical composition of the mushroom Laetiporus sulphureus. Protein content in fruiting bodies is not too high (10.6% d.m.), but the biological value (in vitro digestibility, rate of protein fractions, free amino acid content, etc.) is good (including fat and energy levels). Occurrence of “bioactive” components (phenolics, soluble oligo- and polysaccharides) and the measured free radical scavenging activity are similar to these parameters in Pleurotus (oyster) species. Potassium and phosphorus contents are remarkable (28 940 mg kg−1 d.m. and 4890 mg kg−1 d.m., respectively); levels of some poisonous microelements (As, Cd, Cr) are very low or undetectable. Chicken of the woods (Laetiporus sulphureus) is not only a suitable species for human consumption, but can be a new cultivable mushroom of valuable bioactive substances.