Aspergillus niger NRRL3 was cultivated in a moist wheat bran and ground corncob solid medium supplemented with inorganic minerals for the production of cellobiase (beta-1,4 -glucosidase, EC 3.2.1.21). With this method, A. niger NRRL3 was able to produce a high concentration of cellobiase (215 IU/g of solid substrate) after 96 h of incubation. Temperature and moisture content affected final cellobiase titers. The best conditions for cellobiase production from solid substrate by A. niger NRRL3 were determined to be 70% moisture and 35 degrees C.