In aqueous-methanolic solutions, mushroom tyrosinase was observed to catalyze the oxidation of phenolic moieties of the synthetic polymer poly(4-hydroxystyrene) (PHS). Although oxidation is rapid, on the order of minutes, it seems that only a small number of phenolic moieties of the PHS polymer (1 to 2%) undergo oxidation. Enzymatically oxidized PHS was observed to undergo a subsequent nonenzymatic reaction with aniline yielding an aniline-modified PHS polymer with a low degree-of-substitution. To gain insights into linkages between aniline and oxidized PHS, we characterized products resulting from tyrosinase-catalyzed reactions of p-cresol and aniline. A major product from these small-molecule studies was the Michael＇s-type adduct, 4-anilino-5-methyl-1,2-benzoquinone. Based on similarities in ultraviolet-visible and H-1 nuclear magnetic resonance spectra, we believe Michael＇s-type adducts are present in the aniline-modified PHS polymer. To illustrate the potential utility of this enzymatic approach for grafting PI-IS onto other polymers, we contacted enzymatically oxidized PHS with the amine-containing biopolymer chitosan. Ultraviolet spectra of this chitosan film suggests oxidized PHS is grafted onto chitosan.