The rheological properties of associative polymers (APs) are modified by the presence of surfactants, but little is known about the influence of surfactants on the structure of selfassociated aggregates in aqueous media. Using small-angle neutron scattering (SANS), the structure of self-assembled aggregates of a series in concentration of telechelic poly(ethylene oxide) (M ≈ 20 000 g mol 1) end-capped by hydrocarbon or of fluorocarbon groups in the presence of a fixed amount of sodium dodecyl sulfate (SDS) or lithium perfluorooctyl sulfonate (LiFOS) is investigated. In all systems studied, surfactants and telechelic polymers form mixed aggregates. Their aggregation numbers are reduced and evolve with the concentration of each component. For example, with SDS at 8 mM, the mixed aggregates are composed of 1 AP and 15 SDS or 9 APs and 45 SDS molecules for 1 or 3 wt % of polymer, respectively. The addition of a surfactant enhances the number density of aggregates, which causes the increase of the gel viscosity.