In this paper,Aspergillus niger CU-1 was found to produce maximum amount of α-glucosidase at 88 h while to peak its biomass at 72 h under the best conditions. The pH value of 5.0 was helpful to pile up α-glucosidase. The inoculum of A. niger CU-1 was 10% in a medium contained 25% (w/v) of cassava starch and 3% (w/v) of wheat bran. Then transglucosylation performed for 3.0 d at 160 r/min and 30℃. The pH,reduced sugar,total sugar,biomass (dry weight),and isomaltooligosaccharides (IMOs) were tested. HPLC analysis showed the amount of effective IMOs was higher than 80%,including isomaltose,panose,isomaltotriose,isomaltotetraose,and oligosaccharides with polymerization of 5 or 6. The glucose was about 4%. These results showed that a long period of fermentation with high concentration of substrate was suitable for producing IMOs by A.niger CU-1.