A process for producing a polypeptide, by reacting a peptide component (A) represented by formula (1) below with a peptide component (B) represented by formula (2) below and optionally a compound (C) represented by formula (3) below, to obtain said polypeptide: (1) X-(Pro-Y-Gly).sub.n-OH, wherein: X represents H or the group HOOC--(CH.sub.2).sub.m--CO-- and m denotes an integer of 1 to 18, Y represents Pro or Hyp, and n denotes an integer of 1 to 20; (2) X-(Z).sub.r--OH, wherein X represents H or the group HOOC--(CH.sub.2).sub.m--CO-- and m denotes an integer of 1 to 18, Z represents a peptide chain comprising 1 to 10 amino acid residue(s), and r denotes an integer of 1 to 20; and (3) H.sub.2N--R--NH.sub.2, wherein R represents a linear or branched alkylene group; and further wherein the ratio of the peptide component (A) relative to the peptide component (B) is 100/0 to 30/70 (mol %); provided that in the case where X represents the group HOOC--(CH.sub.2).sub.m--CO-- and m has the same meaning as defined above in formula (1) and/or (2), the amount of compound (C) is substantially 1 mol relative to 1 mol of the total molar amount of peptide component (A) and/or peptide component (B); and in the case where X represents H in the formula (1) and/or (2), the reaction is conducted without compound (C).