Polyelectrolytes are widely used as flocculants for water and waste-water treatment. To better control the flocculation, it is important to understand the structure of the layer of polyelectrolyte adsorbed on a colloidal particle. In the present study, electrophoretic mobilities of polystyrene latex particles with adsorbed polyelectrolytes were analyzed by applying Ohshima-Kondo's theory of soft particles to reveal the structure of the adsorbed polyelectrolyte. Electrophoretic mobilities leveled off to a nonzero value in the limit of high ionic strength of solution, which is a characteristic feature of soft particles. The charge density, ZN [mol/L], in the layer and the length scale parameter of permeability, 1/lambda [nm], were obtained by applying the electrophoretic theory of soft particles. It was found that the mean distance between charged segments of adsorbed polyelectrolytes estimated by ZN was almost the same as 1/lambda.