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Penicillium oxalicum is the well-known major workhorse for cellulase production in industry. But the low β-glucosidase activity in P. oxalicum cellulase leads to inefficiency in biomass degradation and limits its further application, which is a major bottleneck in the efficient biomass conversion by cellulase. Previous study reported genetic transformations of P. oxalicum with homologous bgl genes. While, heterologously expressed beta-glucosidase by genetically modifying host strain could also be an effective tool in developing production of cellulases . In our study, the bgl1 gene of Aspergillus niger was heterologously overexpressed in Penicillium oxalicum. The resulted strain C3-1 showed 156.6- and 245.2-fold increased production of β-glucosidase relative to the parent strain PT3-1 and the wild-type (WT)strain 114-2, respectively. Besides, the filter paper assay of strain C3-1 increased at a factor of 8-folds compared to WT, resulting in levels of up to 3.2 U/ml. In summary, genetically engineering P. oxalicum signifcantly improves β-glucosidase activity, which will ultimately lead to a potent strategy to substantially boost the hydrolytic efficiency of the cellulase cocktail. [ABSTRACT FROM AUTHOR]