A high yield strain Aspergillus niger ZU-07 was used to produce cellobiase. It was found that the spores of A. niger ZU-07 were rich in cellobiase. By entrapping the spores into calcium alginate gels, the cellobiase was immobilized efficiently. The immobilized spores were quite stable, with a half-life 38 days. In repeated batch hydrolysis processes on 10 g l(-1) cellobiose by the immobilized spores, the yield of enzymic hydrolysis remained higher than 97% during 10 batches. In a continuous hydrolysis process, the yield reached 98% at 0.4 h(-1) dilution rate. The cellulosic residue of corncob pretreated with dilute acid was hydrolyzed with cellulase from Trichoderma reesei, the hydrolysis yield was only 69.5% and much cellobiose was accumulated in the hydrolysate. When the hydrolysate was further treated with immobilized spores of A. niger ZU-07, the hydrolysis yield of cellulose was improved to 84.2% because the feedback inhibition caused by cellobiose disappeared, the concentration of total reducing sugar increased from 48.50 to 58.78 g l(-1), and the ratio of glucose in the reducing sugar was increased from 53.6 to 89.5%. The research results are useful in the conversion and utilization of renewable biomass. (C) 2003 Elsevier Ltd. All rights reserved.