The influence of molecular weight on the counterion polarization of sodium polystyrenesulfonate (NaPSS) is investigated by electric light scattering. The polyelectrolyte is adsorbed in excess on beta-ferric hydrous oxide particles (beta-FeOOH), which are shown to assume the charge characteristics of the polymer. Two dispersion regions of the electro-optical effect (below and above 10 kHz) are found to exist due to the polarization of counterions. The high-frequency (HF) effect is attributed to polarization of free counterions along the polymer-coated particle axis and does not depend on the molecular weight of the adsorbed polymer, The amplitude and critical frequency of relaxation of the low-frequency (LF) effect, which is attributed to polarization of bound counterions along the polymer axis, depend on the polyelectrolyte molecular weight. The polarization of bound counterions seems to be responsible for the permanent-like dipole moment behavior of NaPSS at low frequencies of the applied electric field,