AbstractThe complex dielectric constant of collagen in aqueous solutions (polymer concentration,Cp= 0.02–0.2%) was measured at 10°C in the frequency range from 3 Hz to 30 kHz. The loss peak forCp= 0.02% is located at 90 Hz and the dielectric relaxation time τDis estimated to be 1.8 ± 0.3 msec. The τDagrees well with the rotational relaxation time estimated from the reduced viscosity, and the relaxation is ascribed to the end‐over‐end rotation of the molecule. TheCpdependence of τDand the dielectric increment Δε are interpreted in terms of the aggregation of molecules. The dipole moment of a molecule, obtained from Δε atCp= 0.02% and pH 6.5, is (5.2 ± 0.2) × 104D, which is explained by the asymmetrical distribution of the ionized side chains