Incorporating of hydrous ferric oxide (HFO) inside porous supports with large sizes has become an effec-tive way to decontaminate the water from heavy metals. Ubiquitous anions like sulfate are usually pre-sent in high concentrations in water, and might greatly affect adsorption behavior of hybrid HFO. Here, a polymer-based HFO-CPS was fabricated by encapsulating nano-HFO inside a chloromethylated polystyr-ene polymer (CPS) and the reactivity of HFO-CPS with Cu(II) was evaluated in the presence of sulfate ions. Surface complexation theory was firstly employed to describe the effect of sulfate on Cu(II) adsorption edges of hybrid HFO-CPS, where constant capacitance model (CCM) was adopted. The available weak adsorption site ?Fe(2)OH of hybrid HFO-CPS was found to decrease from 20％ Fe to 5％ Fe, which might be caused by the pore plugging effect after HFO encapsulation. With the assumption that a ternary com-plex was formed, the effect of sulfate on Cu(II) adsorption by HFO-CPS were successfully described by CCM using the optimized ?Fe(2)OH site under different sulfate concentrations (1 or 10 mmol?L?1) and Cu/Fe ratios (0.0042 or 0.0252). It is confirmed that the formation of ?FeOHCuSO4 ternary surface com-plexes played an important role in enhancing Cu(II) adsorption on HFO-CPS in the presence of sulfate.