The aim of the presented research was to settle conditions and parameters of Pleurotus ostreatus (Fr.) Kumm. culture and to determine activity and yield of cellulase complexes biosynthesised by this mushroom on different substrates. Wheat straw sterilized by evaporation at temperature 58-60 degrees C during 48 hours was the first substrate. Wheat straw with Reynoutria japonica (Houtt) in 1:1 proportion, sterilized by irradiation (15 kGy), was the second, two-component, substrate. According to the obtained results it can be ascertained that P. ostreatus (Fr.) Kumm. grows and yields well on all kinds of substrates biosynthesising active cellulase complexes E.C. 3.2.1.4. glucohydrolases, both endo- and exogluconase, and E.C. 3.2.1.21. beta-glucosidase.