Alkyl beta-D-xylobioside was prepared by the one-pot reaction of xylan and a fatty alcohol using acetone powder (acetone-dried cells) of Aureobasidium pullulans KK415 (ATCC 201145). Both the yields and reaction speed were significantly increased using the acetone powder compared to those of the cell-free culture filtrate. Using 0.066% acetone powder, 2-ethylhexyl, 1-octyl and 2-octyl beta-D-xylobiosides were produced in the yields of 118, 80 and 74 mg per g xylan, respectively, when alcohol and xylan were incubated at 65 degrees C for 16 h. On the other hand, C8 alkyl xylobioside was hardly produced by the resting cells of A. pullulans.