The peptide catalyst having the amino acid sequence (Z-L-Leu (or Phe)-L-His) was found to be the most stereoselective among the L-histidyl group-containing di-, tri-, or tetrapeptide catalysts in the hydrolysis of enantiomeric amino acid substrates in vesicular membranes. The role of the membrane-assisted hydrophobic interaction between the peptide catalyst and enantiomeric substrates for the improvement of the hydrolysis stereoselectivity was demonstrated by means of direct measurements of nuclear Overhauser effect spectroscopy (NOESY) spectra of the interaction system and by the extremely high stereoselectivity itself obtained by intensifying the membrane-promoted hydrophobic interaction between the catalyst and the substrates.