NOVELTY - Method for producing mutant xylanase catalytic domains, involves substituting a region with respect to the amino acid sequence at positions 118-143 of a 192 amino acid sequence (SEQ ID NO: 2) fully defined in the specification, in the amino acid sequence of the catalytic domains of xylanases with the amino acid sequence at positions 118-143 of SEQ ID NO: 2 or an amino acid sequence exhibiting at least 90% sequence identity to amino acid sequence of SEQ ID NO: 2. The xylanases belongs to the glycoside hydrolase family 11.    USE - The method is useful for producing mutant xylanase catalytic domains which is useful for reducing a saccharification residue adsorptivity of a xylanase and in biomass saccharification agent for saccharifying biomass and producing saccharide (all claimed) used as substitute for biofuel.    DETAILED DESCRIPTION - Method for producing mutant xylanase catalytic domains, involves (a) substituting a region with respect to the amino acid sequence at positions 118-143 of a 192 amino acid sequence (SEQ ID NO: 2) fully defined in the specification, in the amino acid sequence of the catalytic domains of xylanases with the amino acid sequence at positions 118-143 of SEQ ID NO: 2 or an amino acid sequence exhibiting at least 90% sequence identity to amino acid sequence of SEQ ID NO: 2, or (b) substituting a region with respect to the amino acid sequence at positions 144-172 of SEQ ID NO: 2 in the amino acid sequence of the catalytic domains of xylanases with the amino acid sequence at positions 144-172 of SEQ ID NO: 2 or an amino acid sequence exhibiting at least 90% sequence identity to amino acid sequence of SEQ ID NO: 2. The xylanases belongs to the glycoside hydrolase family 11, and the identity of the amino acid sequence of the catalytic domains of the xylanases and the amino acid sequence at SEQ ID NO: 2 is less than 90%. INDEPENDENT CLAIMS are included for the following:    (1) reduction method of saccharification residue adsorptivity of a xylanase;    (2) mutant xylanase catalytic domain;    (3) polynucleotide encoding the mutant xylanase catalytic domain;    (4) vector comprising the polynucleotide;    (5) method for preparing the transformant, involves introducing the polynucleotide, or vector into a host;    (6) transformant comprising the polynucleotide, or vector;    (7) biomass saccharification agent comprising the mutant xylanase catalytic domain, or mutant xylanase; and    (8) method for performing biomass saccharification.