Xylanase of low molecular weight ( K II) was isolated from the fungus Aspergillus niger IBT-90 cultivated in medium with wheat bran. K II was purified by precipitation with ammonium sulphate ( 20 - 80% saturation) and gel filtration on Biogel P-10. This enzyme is most active in hydrolysis of birchwood xylan at 50 degrees C and pH 5.5. Xylanase K II has an ability to degrade 1,4-beta-bonds and to debranch substrates. It degrades not only xylans but also cellulose, an important factor for its application in bakery. Ag+, Fe3+ and NBS are strong inhibitors of the enzyme. DTT and Na+ activate xylanase K II by 24 and 13%, respectively. Enzyme K II used as additive to flour improves dough properties, increases the volume of wheat - rye and whole meal bread, and increases the porosity of crumb and the moisture of the final product, consequently extending the shelf life of bread.