Abstract: A fluorescent protein sensor capable of quantitatively measuring oxidation degree of methionine residues of a specific protein, and a use thereof. Specifically, a fluorescent biosensor recombinant protein in which an MsrB protein, a cpYFP protein, a thioredoxin 3 protein, a linker protein and a G protein are linked in this order, and which is capable of quantitatively measuring the oxidation degree of methionine residues of a target protein; a fluorescent biosensor comprising same; a method for measuring oxidation degree of methionine residues of a target protein; and an information providing method for diagnosis of oxidative stress-associated diseases; and a method for screening for a therapeutic agent for oxidative stress-associated diseases.