Site-specific, covalent immobilization of protein is of great importance in the design of bioanalytical devices. User-defined covalent coupling of protein onto the surface has been primarily limited to a noncanonical amino acid or cysteine residues. It is desirable to develop a new approach for site-specific biofunctionalization. Herein, we demonstrate a robust and modular chemoenzymatic approach for site-specific, covalent grafting of proteins onto a surface. The synthetic strategy relies on the combination of surface amine functionalization, followed by sortase-mediated coupling. The developed method was validated by site-specific immobilization of two model proteins (glutathione S-transferase and green fluorescent protein) on cellulose and polydimethylsiloxane surfaces via a short recognition motif (LPETG). The covalent coupling of immobilized proteins at the interface was characterized by Fourier Transform Infrared Spectroscopy in attenuated total reflectance mode, X-ray photoelectron spectroscopy, atomic force microscope, and fluorescent microscopy. This enzymatic surface functionalization approach could permit an oriented, homogeneous, and site-specific covalent tethering of LPETG-tag proteins to other materials under mild conditions.