Abstract: In order to optimize the hydrated ferric oxide (HFO) loadings of acrylic resin-based HFO composite adsorbents, five composite adsorbents were prepared by regulating FeCl₃ concentration, and the HFO loadings were 5.3wt%, 8.6wt%, 12.1wt%, 14.9wt% and 18.5wt% (mass fraction in Fe), respectively. The structure properties of composite adsorbents were analyzed. Furthermore, the adsorption performance of composite adsorbents in removing phosphate were investigated, including adsorption isotherms, adsorption kinetics, effect of pH and coexisting anion, and elution effect. The results show that HFO nanoparticles dispersed into composite adsorbents are amorphous in nature, and the radial distribution of HFO obeys U-type distribution. Moreover, the phosphate adsorption capacity increases with the HFO loadings and then decreases, and the adsorption capacity of the composite adsorbent with HFO loading of 14.9wt% is the maximum (19.04 mg·g⁻¹). The contact time of 240 min is long enough for composite adsorbents to achieve adsorption equilibrium, and the adsorption kinetic curves of the composite adsorbents are fitted well with pseudo-first order kinetic model (R²>0.99). The optimal pH for phosphate adsorption is 6~8. Furthermore, there is no phosphate adsorption by resin when the concentration of SO₄²⁻ is equal or greater than 600 mg·L⁻¹, while it does not pose any noticeable effect on phosphate adsorption by the loaded HFO nanoparticles. The regeneration efficiencies approach 100% by a binary 5wt% NaOH and 5wt% NaCl solution during 4 continuous adsorption-regeneration cycles. The experiments show that the phosphate adsorption capacity of the composite adsorbents increases with the HFO loadings and then decreases, while there is no significant difference in structure property, adsorption equilibrium time, pH range, effect of coexisting anion, and elution effect.