What is aimed at is provision of an inexpensive and efficient saccharificationmethod forlignocellulose using a thermostable xylanase and provision of a mutantxylanase that has asubstitute amino acid residue, and that exhibits stable activity even undersevere conditions inwhich enzymes easily inactivate, and that provides an initial rate of reactionnot significantlyreduced as compared to a wild-type xylanase corresponding to the mutantxylanase.Provided is a method of producing a saccharified product of lignocellulose,includingcontacting a lignocellulosic raw material with a thermostable xylanase, and amutant xylanasethat provides an initial rate of reaction that is at least 70% of thatprovided by a wild-typexylanase corresponding thereto, that has a xylanase activity after heattreatment at 50 °C for24 hours that is at least 50% of its xylanase activity before the heattreatment, and that has asubstitute amino acid residue.
