Alkyl beta-D-xylobioside and alkyl beta-D-xyloside were prepared by the one-pot reaction of xylan and a fatty alcohol, such as 1-octanol, 1-decanol, 2-octanol and 2-ethylhexanol using the cell-free culture filtrate of the xylan-assimilating strain, Aureobasidium pullulans KK415. Using this strain, a novel surfactant, alkyl beta-D-xylobioside, was produced as the main product when the alcohol and xylan was incubated at a temperature of 65 degrees C and pH 4.5.