The octadecyl esters of L-phenylalanine, L-tyrosine and L-tryptophan were synthesized to elucidate the relationships among the molecular arrangements, polycondensation in the monolayers and the conformations of the resultant polyamino acids. It is found that the polycondensation of the derivatives occurred easily in the monolayers where the functional groups were appropriately arranged. The copper (II) ion in the subphase changed the packing of monolayers by complex formation and thus greatly accelerated the polycondensation, Upon polycondensation, polyamino acids with mixed conformations of alpha-helix, random coil and beta-sheet were formed. Copper (II) ion in the subphase not only markedly promoted the polycondensation but also favored the formation of polyamino acids with beta-sheet conformation, Possible mechanisms were proposed to explain the results.