AbstractThe Raman spectra of poly‐L‐hydroxyproline in the solid state and aqueous solution have been obtained. From the spectra, the conformations of the polypeptide in the solid and aqueous solution are found to be the same. Major differences in the spectra between the solid and solution are traced to environmental influences of the pyrrolidine group as indicated by studies of the monomers. The Raman spectra of the imino acids, proline and hydroxyproline, as the dipolar ions, the hydrochlorides, and the sodium salts are also reported.