The production of cellulases and xylanases by Trichoderma viride L-333 was studied. Significant amounts of extracellular enzymes were obtained when submerged fermentation was performed in the fed-batch regime on cellulose-and xylan-based media with addition of sophorose and Tween-80. The culture filtrate of T. viride was used for enzymatic treatment of recycling newspaper (TMP) fibers. To elucidate the mechanism of the enzymatic hydrolysis, the fractionation and separate processing of tree different fiber size fraction were performed. The biological processing of recycling fiber caused an increase in brightness and dewatering properties. The most significant improvement was observed with unfractionated and long fiber fractions at a ratio of cellulase to endoglucanase to xylanase of 1:10:100.