The adsorption of binary mixtures of poly(vinylpyrrolidone) (PVP) and sodium dodecyl sulfate (SDS) and of ternary mixture of PVP, SDS, and pentaethylene glycol monodecyl ether (C10E5) onto silica has been studied by the measurements of the adsorbed amount of PVP and the heat of adsorption. The amount of PVP adsorbed from the binary mixtures decreases as the SDS concentration is increased, whereas the enthalpy change passes through a maximum at SDS concentration of ca. 4 g/L. The chain conformation of PVP adsorbed on silica has been estimated from the adsorption data in relation to the surfactant concentration. It changes from loops and tails to trains upon increasing SDS concentration. At SDS concentrations higher than 4 gn, a comblike conformation is observed. The adsorption of PVP/SDS/C10E5 ternary mixtures depends on the polymer concentration regime.