A transglucosidase of Aspergillus niger had hydrolysis and transglucosylation activities toward several types of malto- and isomalto-oligosaccharides. The activity was competitively inhibited by glucose and mannose but was not inhibited by galactose and fructose. The K(i)s of glucose and mannose were 12.9 mM and 75.9 mM, respectively. The enzyme was stable in storage at -20 degrees C with 60% (v/v) glycerol and 4 degrees C for at least 40 days.