Star-like amphiphilic polyacrylamide (SHPAM), consisting of nano-SiO2 as the core and a layer of amphiphilic chains as the shell, having two gradient molecular weights, was prepared via a facile method. To elucidate its enhanced oil recovery (EOR) potential, the viscoelastic flow and displacement efficiency of SHPAM were studied using geological rock core samples. The results showed that the core-shell microstructure and intermolecular interactions imparted viscoelasticity to SHPAM in a lower-concentration region. The elasticity mechanism of SHPAM solutions in porous media was determined by quantifying the relaxation time. Low-field nuclear magnetic resonance experiments suggested that SHPAM flowed through the dominant porous media followed by intermediate porous media having radii of 0.08-10.0 mu m. The thickness of the adsorbed layer was independent of the shear rate, demonstrating that SHPAM was compatible with porous media owing to the reversibly viscoelastic flow. The core flooding tests demonstrated that even after hydrolyzed polyacrylamide flooding, 3.0% oil saturation was further recovered by SHPAM flooding even in a region with low capillary number (<10(-5)). Moreover, over 27% oil recovery with 70% cumulative oil recovery was achieved with a SHPAM pore volume of 0.3 and concentration of 1500 mg/L. The displacement efficiency tests confirmed that the high viscoelasticity of SHPAM imparted anomalous enhanced oil recovery efficiency to the HPAM. (C) 2018 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.