The microorganism Aspergillus niger CCRC 31494 can produce an extracellular glucosyltransferase (GTase, EC 2.4.1.24) with a high transglucosylating activity. The maximal enzyme production occurred at initial maltose concentration of 40 g l(-1). The microorganism was also grown in a 5-liter jar fermenter for GTase production. It was found that the optimal agitation and aeration rates were 750 rev min(-1) and 1.0 l min(-1), respectively, and the enzyme production was about 0.25-0.26 units ml(-1).