The genetic library of alpha-helical amphipathic peptides, 20 amino acid long, was designed and expressed under the T7 promoter in the E. coli JM 109(DE3) and BL21 (DE3). Clones that inhibited the growth of the host cell were screened by the relative size of colonies on the plates. Clones which strongly inhibited growth of Escherichia coli JM 109(DE3) were further selected. The method developed in this study is useful for the structure activity relationship study of antimicrobial peptides.