<P><B>Graphical abstract</B></P><P><ce:figure id='fig0005'></ce:figure></P><P><B>Highlights</B></P><P>► Hyperthermostable xylanase was expressed in <I>Pichia pastoris</I> by optimization of codon. ► A protein concentration of 10.1gl<SUP>−1</SUP> was secreted with activity of 40,020Uml<SUP>−1</SUP>. ► The xylanase displayed optimal activity at 100°C and pH 5.5. ► The <I>P. pastoris</I> is a good candidate for hyperthermostable xylanase production.</P> <P><B>Abstract</B></P><P>The second xylanase gene (<I>xynB</I>) from the hyperthermophilic <I>Thermotoga maritima</I> was optimized according to the codon usage of <I>Pichia pastoris</I> and expressed in <I>P. pastoris</I>. The optimized gene (<I>xynBop</I>) shared 77.8% of nucleotide sequence identity with that of native gene. A total of 232 nucleotides were changed and the G+C ratio was simultaneously increased from 42.7% to 43.1%. The recombinant xylanase (XynBop) was secreted into the culture medium that reached a total extracellular protein concentration of 10.1gl<SUP>−1</SUP> with an activity of 40,020Uml<SUP>−1</SUP> in 5-l fermentor culture. The recombinant enzyme was optimally active at pH 5.5 and at 100°C, respectively. The secreted expression level makes the enzyme a good candidate for hyperthermostable xylanase production.</P>