AbstractSome measurements of the electrophoretic velocity were carried out on sodium polyvinyl alcohol sulfates. The intrinsic mobility of the polyion in sodium chloride solutions was obtained by extrapolating the values at various polymer concentrations. The extrapolating value at the zero polymer concentration was the same for both descending and ascending boundaries. The mobility of polyion vs. sodium chloride concentration curve thus obtained showed the following features. (a) At zero NaCl concentration the mobility of polyion quite agrees with the mobility of the monomer acid. (b) In the limit of sufficiently concentrated NaCl solution, the mobility also approaches the mobility of the monomer acid. (c) In the intermediate state between these two limits, measured mobilities of polyion are always larger than the mobility of the monomer acid. Accordingly, there is a maximum of the mobility at a certain NaCl concentration. These experimental results were analyzed in terms of the theory of Hermans and Fujita on the electrophoresis of coiled polyelectrolyte, and it was found that their theory gives a satisfactory (at least qualitatively) explanation of our experimental data.