A recoverable and thermoresponsive polymer-protein bioconjugate is synthesized and employed in the purification of protein with free sulfhydryl groups. Initiator with disulphide was modified on the cysteine residue of the target protein. Poly(N-isopropylacrylamide) exhibiting a lower critical solution temperature was grown from the protein. The resulting protein-polymer conjugate was successfully thermoprecipitated and separated from other proteins. The approach was demonstrated with bovine serum albumin with the recycling yield of 76.4%. Enzyme activity test with papain verified the reversible polymer modification protected protein under extreme environments without affecting the functionality of the protein. This study implies the favorable potential of chemo-selective enriching and purification of proteins.