Provided are modified beta-glucosidase enzymes, derived from the Trichoderma reesei Cel3A beta-glucosidase, that exhibit improvements in one or more kinetic parameters (KG, KG2, kcat) comprising amino acid substitutions at one or more of positions 43, 101, 260 and 543. Also provided are genetic constructs comprising nucleotide sequences encoding for modified beta-glucosidase enzymes, methods for the production of modified beta-glucosidase enzymes from host strains and the use of the modified beta-glucosidase enzymes in the hydrolysis of cellulose.