Neutral and acidic oligosaccharides were obtained from birchwood xylan by treatment with an endoxylanase, family 11 class, from Sporotrichum thermophile. The main acidic xylooligosaccharide (aldopentauronic acid) was separated from the hydrolysate by anion-exchange and size-exclusion chromatography and the structure was determined by 13C NMR spectroscopy. The aldopentauronic acid yield was 25% (w/w) of the total solubilized sugars. The addition of purified aldopentauronic acid at a concentration of 5 mg/l to cucumber liquid culture in 2.5-l airlift bioreactors caused in increase in both the number of regenerants and their fresh weight.