The xylanaseB (XynB) (JX560731.1) gene of Aspergillus niger IA-001 was optimized according to the codon usage of Pichia pastoris and expressed in P. pastoris GS115. The optimized XynB expression level was increased 2.8 times relative to that of the wild-type XynB, and the dual-copy XynB (optimized) expression level was increased 1.9 times relative to that of the single-copy XynB (optimized). The activity of the dual-copy XynB ((XynB-opt)(2)) was maximized at 15,158.23 +/- 45.11 U/mL after 120 h of shaking. The optimal temperature and pH of (XynB-opt)(2) were 50 A degrees C and 5.0, respectively. (XynB-opt)(2) showed a high specific activity of 6,853.00 A +/- 20.08 U/mg. IC analysis of the standard xylooligosaccharides showed that (XynB-opt)(2) was an endo-xylanase with X2 as the main degradation product. (XynB-opt)(2) was highly specific towards different natural xylans. After 24 h of hydrolysis, more than 90 % of the total hydrolysis products of xylan were X2 and X1, almost no X4 similar to X6. In addition, the enzyme exhibited resistance to many metal ions and low pH values. The superior catalytic properties of (XynB-opt)(2) suggested its great potential as an effective additive in animal feed industry.