A combined enzymatic treatment/acid hydrolysis technique was utilized to synthesize cellulose nanocrystals (CNCs) from sugar beet pulp. CNCs were functionalized with magnetite nanoparticles and dopamine making a versatile nano-carrier (DA/Fe3O4NPs@CNCs) for covalent enzyme immobilization. Oxygene/amine functionalities, high magnetization value, and specific surface area of DA/Fe3O4NPs@CNCs made it a reusable and green candidate for conjugation to hydrolytic enzyme cocktails (three cellulases, two hemicellulases, and their combinations) to prepare an innovative and practical nano-biocatalyst for biomass conversion. The conjugated enzymes showed an enhanced optimum temperature (∼ 10 °C), improved thermal stability, and shifted optimum pH toward alkaline pHs. Covalent attachment could successfully suppress the enzyme leaching and provide easy recovery/reuse of the nano-biocatalyst up to 10 cycles, with > 50% of initial activity. Application of the nano-biocatalyst in hydrolysis of rice straw and sugar beet pulp showed an increase (20-76%) in the yield of fermentable sugars compared to the free enzyme cocktails.