Catalyzes the hydrolysis of beta-1,3-xylan into oligosaccharides, mainly xylotriose and xylobiose with smaller amounts of xylotetraose, xylose, xylopentaose and xylohexaose. Weakly active toward beta-1,3-xylotriose, yielding xylose and xylobiose. Converts beta-1,3-xylotetraose into xylotriose, xylobiose and xylose. Converts beta-1,3-xylopentaose into xylotetraose, xylotriose, xylobiose and xylose. Does not hydrolyze xylobiose, p-nitrophenyl-beta-xyloside, beta-1,4-xylan, curdlan or carboxymethylcellulose. Random hydrolysis of (1->3)-beta-D-glycosidic linkages in (1->3)-beta-D-xylans. Completely inhibited by Cu(2+), Hg(2+) and N-bromosuccinimide. Strongly inhibited by Ag(+), Zn(2+) and Pb(2+). Moderately inhibited by Fe(3+), Al(3+), Mn(2+), dithiothreitol and p-chloromercuribenzoic acid. Slightly activated by Mg(2+) and Ca(2+). Unaffected by Na(+), K(+), Ba(2+), EDTA, iodoacetic acid and N-ethylmalaimide. Optimum pH is 7.0. Stable between pH 5.0 and 8.0. Optimum temperature is 37 degrees Celsius. Stable below 30 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.