A remarkable increase of multidrug-resistant bacteria has become a serious threat to public health threat. The amphiphilic antibiotics that attack bacterial membranes are promising agents for combating bacterial pathogens. Among them, cyclic decapeptide gramicidin S (GS), cyclo(-Val-Orn-Leu-D-Phe-Pro)2, are attractive targets for drug discovery. GS possesses the strong antibiotic activity against Gram-positive bacteria and weak antibiotic activity against Gram-negative bacteria. In addition, no resistance has been found for the antibiotics, because it requires significant alteration of the lipid composition of the cell membrane.