The family 10 xylanase (XynB) from Thermotoga maritima MSB8 is extremely thermostable and great potential in the applications of various fields of industry. The gene mxynB(64) was amplified by the method of PCR with the template of the genomic DNA of Thermotoga maritima MSB8, and cloned into the expression vectors of Escherichia coli and Pichia pastoris respectively. Xylanase B(40kD) was successfully expressed by the two heterologous protein expression systems with high-level production. The recombinant protein of XynB expressed in Pichia pastoris showed extreme thermostability and pH stability, which was optimally active at 90 degrees C and quite stable over the pH range of pH 5.0-10.8 at 70 degrees C. After incubation of the enzyme at 100 degrees C for 30 min, XynB retained 70% higher residual activity. The recombinant XynB expressed in Pichia pastoris is of great use in a variety of industrial and agricultural applications.