Peptides may be produced by using (A) a first amino acid or peptide, which is converted into its ionic liquid form through the formation of an ionic bond, as a substance serving as both a reaction solvent and a reaction starting material and reacting the first amino acid or peptide with (B) an ester of second amino acid or peptide, in the absence of any peptide hydrolase or any condensation agent, in the presence of water in an amount of not more than 20% by mass relative to the total mass of the reaction system to form a peptide bond between the first amino acid or peptide and the second amino acid or peptide. By means of this process, it is possible to synthesize a peptide at a high concentration and at a high yield, and this method is excellent for producing peptides on an industrial scale.
