The present invention provides a novel polypeptide or polypeptide derivative which has no risk of infection with a pathogen or propagation of a pathogenic factor and of an undesirable side effect, and which is useful as a carrier of various biologically-active substances or apatite, as well as a process for producing the same. More particularly, the present invention provides a polypeptide comprising a peptide unit having an amino acid sequence represented by the formula: -Pro-X-Gly- (wherein X represents Pro or Hyp) and a peptide unit having an amino acid sequence represented by the formula: -Pro-Hyp(O—Y—Z)-Gly- (wherein Y represents a carbonyl group, a saturated or unsaturated hydrocarbon group with or without a carbonyl group, or a saturated or unsaturated hydrocarbon group with or without a carbonyl group, including an aromatic group, and Z represents a carboxyl group), as well as a process for producing the same.