Protein-based hydrogels have attracted considerable interests due to their potential applications in biomedical engineering and material sciences. Using a tandem modular protein (GB1)(8) as building blocks, we have engineered chemically cross-linked hydrogels via a photochemical cross-linking strategy, which is based on the cross-linking of two adjacent tyrosine residues into dityrosine adducts. However, because of the relatively low reactivity of tyrosine residues in GB1, (GB1)(8)-based hydrogels exhibit poor mechanical properties. Here, we report a Bolton-Hunter reagent-based, facile method to improve and tune the mechanical properties of such protein-based hydrogels. Using Bolton-Hunter reagent, we can derivatize lysine residues with phenolic functional groups to modulate the phenolic (tyrosine-like) content of (GB1)(8). We show that hydrogels made from derivatized (GB1)(8) with increased phenolic content show significantly improved mechanical properties, including improved Young's modulus, breaking modulus as well as reduced swelling. These results demonstrate the great potential of this derivatization method in constructing protein-based biomaterials with desired macroscopic mechanical properties.