We prepared a photoresponsive amphiphilic sequential polypeptide, (M) over bar(n) = 10 630, composed of two amphiphilic a-helical copolypeptides, poly[(gamma-methyl L-glutamate)-co-(L-glutamic acid)], jointed by an azobenzene as a model of photoreceptors. We investigated the photoinduced structural and functional changes of the photoresponsive polypeptide in an aqueous solution and a dipalmitoylphosphatidylcholine bilayer membrane system, respectively. In the dark, the photoresponsive amphiphilic sequential polypeptides formed a micelle in aqueous solution and a transmembrane bundle in the bilayer membrane, respectively. The transmembrane bundle in the membrane acted as an ion permeable path. UV light irradiation induced a bending of the polypeptide by a trans-cis photoisomerization of the azobenzene moiety. The photoinduced structural changes of the polypeptide resulted in a disaggregation of the micelle in aqueous solution and a destabilization of the transmembrane bundle, respectively. The behavior arose from a photoinduced denaturation of the amphiphilic character of the polypeptides. After removal of the light, the initial micellar aggregate in aqueous solution did not recover. However, the polypeptides in the membrane returned to the original transmembrane bundle structure. As a result, photoinduced reversible structural changes of the polypeptide in the bilayer membrane could regulate a transmembrane ion transport.