We engineered a disulphide bridge between two adjacent double-layered β-sheet at the N-terminal region of Trichoderma reesei endo-1,4-β-xylanase II(XYN II) by site-directed mutagenesis. The native xylanase XYN-OU and the mutated xylanase XYN-HA12 (T2C, T28C and S156F) were separately expressed in Pichia pastoris. Both xylanases were purified and characterized. The optimum temperature of XYN-HA12 was increased from 50°C to 60°C, relative to XYN-OU. At 70°C, the halftime of inactivation for XYN-OU and XYN-HA12 were 1 min and 14 min, respectively. The optimum pH of XYN-HA12 was 5.0, similar to XYN-OU. However, XYN-HA12 could retain over 50% activity from pH 3.0 to 10.0 at 50°C for 30 min. As for XYN-OU, it could retain over 50% activity from the pH value 4.0 to 9.0 at 50°C in 30 min. The result of the mutated xylanase indicated that constructed disulphide bridge could improve its thermostability at relatively higher temperature.