AbstractThe poly‐L‐lysine‐ (PLL) and poly‐DL‐lysine‐copper(II) complexes were used as the catalysts for the oxidation of 3.4‐dihydroxyphenylalanine. The catalytic activity of poly‐L‐lysine‐copper(II) complex (PLL‐Cu(II)) was found to be larger than that of bis(ethylenediamine)‐copper(II) at both pH 6.9 and 10.5. The catalytic activity was discussed on the basis of some kinetic data. The oxidation was presumed to proceed through the formation of a reaction intermediate between the catalyst and the substrate. It was also revealed that the oxidation was catalyzed asymmetrically when the PLL‐Cu(II) was used as the catalyst at pH over 10.5. The asymmetric oxidation was presumed to be ascribed to the helical structure of PLL‐Cu(II) in the