A short collagen model polypeptide, (L-prolyl-L-prolylglycyl)(5) (PPG5), behaves as a fully dissociated flexible zwitterionic polymer chain in pure water. Its first and third normal modes of chain conformational fluctuation were detected as distinct dielectric relaxation modes. Addition of acetic acid at 30 mM to an aqueous solution of PPG5 effectively Suppressed the overall relaxation strength by protonation of the carboxy termini of the polypeptide. Furthermore, the hydration number per PPG5 molecule was determined to be 130 by dielectric relaxation (DR) spectroscopy over a frequency range from 1 MHz to 20 GHz; this value was not affected by the addition of acetic acid.