The effect of a polyelectrolyte, poly(styrenesulfonate sodium) (PSS), on poly(ethylene oxide) (PEO) adsorption on the polystyrene latex (PSL) particle/water interface at different sodium chloride (NaCI) concentrations has been investigated by small-angle neutron scattering (SANS). Our study shows that in the absence of NaCl or with a low NaCl concentration, PSS forms a complex with PEO in the bulk Solution and therefore strips PEO off from the latex particle surface because of the electrostatic repulsion between the latex particles and the PEO/PSS complexes. With increasing NaCl concentration, the electrostatic repulsions between the PEO/PSS complexes and PSL particles are reduced. and at the same time, PFO/PSS complexes break down and PEO adsorption is enhanced. With a further increase in NaCl concentration, PSS itself starts to adsorb on the PSL particles and competes with the PEO adsorption, which is then reduced.