The invention provides for a polypeptide, which is useful as a biomaterial and free from infection. The polypeptide comprises a peptide unit of formula (1), and optionally one or more units of formulae (2) to (3): (1) [--(OC--(CH.sub.2).sub.m--CO).sub.p-(Pro-Y-Gly).sub.n-].sub.a; (2) [--(OC--(CH.sub.2).sub.m--CO).sub.q-(Z).sub.r-].sub.b; and (3) [--HN--R--NH--].sub.c, wherein "m" is 1-18 , "p" and "q" are identical or different, and each is 0 or 1 , "Y" is Pro or Hyp, and "n"1-20 ; "Z" is a peptide chain comprising 1-10 amino acids, "r"1-20 , and "R" is a linear or branched alkylene group; the molar ratio of "a" to "b"[a/b] is 100/0 to 30/70 ; when p=1 and q=0, c=a, when p=0 and q=1, c=b, when p=1 and q=1, c=a+b, and when p=0 and q=0, c=0; and the polypeptide shows a peak of molecular weight in a range from 1.times.10.sup.4 to 100.times.10.sup.4 in the molecular weight distribution.