In this Letter, the effect of addition of poly(ethylene oxide) (PEO) on the nature of the self-assemblies of sodium dodecyl sulfate (SDS) and branched poly(ethyleneimine) (PEI) is investigated. We demonstrate that the neutral polymer adsorbs onto the surface of the polyetectrolyte/surfactant nanoparticles, which may result in sterically stabilized colloidal dispersions of the nanoparticles with hydrophobic core and hydrophilic corona. The kinetic stability is maintained even at high ionic strengths, where the charge stabilization of the PEI/SDS dispersions is inefficient. These results might be exploited to improve the efficiency of those formulations, which contain oppositely charged macromolecules and amphiphiles.