Catalyzes the hydrolysis of beta-1,3-xylan into oligosaccharides, mainly xylotriose and xylobiose with smaller amounts of xylotetraose, xylose, xylopentaose and xylohexaose. Does not hydrolyze xylobiose, p-nitrophenyl-beta-xyloside, beta-1,4-xylan, carboxymethylcellulose, curdlan, glucomannan or beta-1,4-mannan. Random hydrolysis of (1->3)-beta-D-glycosidic linkages in (1->3)-beta-D-xylans. Completely inhibited by CuCl(2), FeCl(3), HgCl(2) and N-bromosuccinimide. Moderately inhibited by AgCl, AlCl(3), Pb(CH(3)COO)(2) and dithiothreitol. BaCl(2), CaCl(2), KCl, MgCl(2), MnCl(2), NaCl, ZnCl(2), ethylenediaminetetraacetic acid, N-ethylmaleimide, iodoacetic acid and p-chloromercuribenzoic acid have little or no effect on activity. Optimum pH is 7.0-7.5. Stable from pH 5.0-11.0. Retains 65% and 70% of activity respectively when incubated at pH 4.0 and 12.0 for 24 hours. Optimum temperature is 40 degrees Celsius. Stable below 40 degrees Celsius. Loses 70% and 99% of activity respectively when incubated for 10 minutes at 50 and 60 degrees Celsius. By beta-1,3-xylan. The carbohydrate binding module (CBM) binds to insoluble beta-1,3-xylan, but not to insoluble beta-1,4-xylan, beta-1,4-glucan, beta-1,4-mannan, curdlan, chitin, or soluble polysaccharides. Belongs to the glycosyl hydrolase 26 family.