In filamentous fungi, the expression of secretory glycoside hydrolase encoding genes, such as those for amylases, cellulases, and xylanases, is generally repressed in the presence of glucose. CreA and CreB have been observed to be regulating factors for carbon catabolite repression. In this study, we generated single and double deletion creA and/or creB mutants in Aspergillus oryzae. The alpha-amylase activities of each strain were compared under various culture conditions. For the wild-type strain, mRNA levels of alpha-amylase were markedly decreased in the later stage of submerged culture under inducing conditions, whereas this reduced expression was not observed for single creA and double creA/creB deletion mutants. In addition, alpha-amylase activity of the wild-type strain was reduced in submerged culture containing high concentrations of inducing sugars, whereas all constructed mutants showed higher alpha-amylase activities. In particular, the alpha-amylase activity of the double deletion mutant in a medium containing 5 % starch was > 10-fold higher than that of the wild-type strain under the same culture conditions. In solid-state cultures using wheat bran as a substrate, the alpha-amylase activities of single creA and double deletion mutants were > 2-fold higher than that of the wild-type strain. These results suggested that deleting both creA and creB resulted in dramatic improvements in the production of secretory glycoside hydrolases in filamentous fungi.