A new ion-imprinted polymer (IIP) was synthesized by thermal copolymerization of bis(2-methacryloxyethyl) phosphate as functional ligand and ethylene glycol dimethacrylate as cross-linker in the presence of Th⁴⁺ as a template ion. The molar ratio of the functional ligand to Th⁴⁺ was optimized to be 4 by ³¹P NMR titration, elemental analysis, and EXAFS, which was verified by comparing the adsorption capacities and selectivities of IIPs with different composition. Thorium(IV) ions were leached out using 0.1 mol L⁻¹ ethylenediaminetetraacetic acid disodium salt and the prepared IIP was characterized by infra-red spectroscopy, thermogravimetric analysis and Brunauer–Emmett–Teller surface area measurement. It was found that the IIP could extract Th⁴⁺ from high acidity solution. The maximum adsorption capacity was as high as 33.3 mg g⁻¹ in 1.0 mol L⁻¹ HCl. Even in 6.0 mol L⁻¹ HCl, its adsorption capacity was still considerable. Moreover, the IIP exhibited good selectivity towards Th⁴⁺, especially in the presence of competing ions such as La³⁺, Eu³⁺, Yb³⁺, UO₂²⁺, and Fe³⁺.