Xylanase J (XynJ) of alkaliphilic Bacillus sp. strain 41M-1 is a multi-domain enzyme and consists of a glycoside hydrolase (GH) family 11 catalytic domain and an additional xylan-binding domain (XBD) belonging to carbohydrate-binding module (CBM) family 36. Random mutations were introduced into the XBD gene and the repertoire was cloned for display on the surface of filamentous phage. The mutant XBD with amino acid substitution T316I (Thr317 was replaced by Ile) showed higher xylan-binding activity compared to the wild-type XBD. Furthermore, hydrolyzing activity of XynJ toward insoluble xylan was also improved by introducing the mutation T316I.