Xylanases have been the focus of research owing to their industrial potential in animal feed production, food processing and pulp and paper processes. In order to obtain insight into the structural stability of family 11 xylanases, the mesophilic family 11 xylanase (beta-1,4-xylan xylanohydrolase; EC 3.2.1.8) from Bacillus subtilis 1A1 has been crystallized and diffraction data have been collected to 1.7 A. The crystals belong to the orthorhombic space group P2(1)2(1)2, with unit-cell parameters a = 50.93, b = 70.50, c = 40.05 A. The structure has been determined by molecular replacement, resulting in a crystallographic residual of 36.4% after rigid-body refinement.