The effect of surfactants on the adsorption properties of ethyl(hydroxyethyl)cellulose (EHEC) and its hydrophobically modified analogue (HM-EHEC) at the solid−liquid interface has been studied by ellipsometry. The adsorption characteristics of EHEC and HM-EHEC without the presence of surfactants are also presented. The polar silica surface and a hydrophobized silica surface were used as substrates. On the polar silica surface, a small addition of the anionic surfactant sodium dodecyl sulfate (SDS) caused a 3- to 5-fold expansion of the preadsorbed EHEC or HM-EHEC layers, while the adsorbed amount was less influenced. On the hydrophobized silica surface, SDS could replace EHEC (>10 mM SDS), while some adsorbed HM-EHEC still could be detected well above the critical micelle concentration of SDS in the bulk (14 mM). The nonionic surfactant octa(ethylene oxide) dodecyl ether (C12E8) did not affect the adsorbed layer structure on silica, and the cationic surfactant cetyltriammonium chloride (CTAC) on hydrophobized silica showed similar effects as SDS but with a smaller magnitude. It is proposed that the adsorbed layer structure mainly is governed by polymer−surfactant interfacial interactions.