Surface charging of polystyrene latex particles stabilized with sodium dodecyl sulfate (SDS) was investigated. The surfactant adsorption isotherm and electrophoretic mobilities of monodisperse latex particles were measured. Electrophoretic mobility measurements at moderate ionic strengths (around 0.1 M) indicated a substantial degree of counterion binding to adsorbed dodecyl sulfate anions, comparable to that found in SDS micelles. We offer a consistent description of surface charging of SDS-stabilized latex particles and SDS micelles taking into account binding of sodium counterions to dodecyl sulfate anions.