Penicillium decumbens T. is an important filamentous fungus for the production of cellulases to effectively degrade lignocellulose for second generation biofuel production. In order to enhance the capability of Penicillium decumbens to produce cellulases, we constructed a creB (a deubiquitinating enzyme encoding gene) deletion cassette, and generated a creB knockout strain with homologous double crossover recombination. This mutation resulted in a detectable decrease of carbon catabolite repression (CCR) effect. The filter paper activity, endoglucanase activity, xylanase activity and exoglucanase activity of the deltacreB strain increased by 1.8, 1.71, 2.06 and 2.04 fold, respectively, when comparing with the parent strain Ku-39. A 2.68 fold increase of extracellular protein concentration was also observed. These results suggest that the deletion of creB results in CCR derepression. These data also suggest that CREB influences cellulase production of Penicillium decumbens. In generation, this study provides information that can be helpful for constructing cellulase hyper-producing strain.