To improve the efficiency of mobility control for polymer flooding, a novel thickening system was formed by adding medium-chain fatty alcohols to hydrophobically modified polyacrylamide (HMPAM) brine solutions. The interaction of HMPAM with fatty alcohols was investigated in terms of rheology properties, aggregate microstructure, and mobility control ability. The results show that n-octanol (C8OH) generates the best synergistic behavior with HMPAM compared to other fatty alcohols. More hydrophobic groups initially existing in either intramolecular or intermolecular association reassemble into larger aggregation structures due to the presence of C8OH. 750 mg.L-1 C8OH could lead to an increase of viscosity by four times as that of individual HMPAM at low polymer concentration (1000 mg.L-1). Owing to the enhancement of the association structure, the HMPAM + C8OH system displays stronger shear-thinning behavior, higher viscoelasticity, and better resistance to salt and temperature. Polymer-brine displacement tests indicate that compared to other systems HMPAM + C8OH exhibits higher effective viscosity and moderate polymer retention in porous media, showing promising applicability in efficient mobility control for low-concentration polymer flooding.