The enhancement of copper (Ⅱ) adsorption on kaolinite in the presence of humic acids under acidic conditions, in particular near the neutral pH range of pH 5～6, was investigated. In the experiment, the addition of humic acids increased the adsorption percentage of copper (Ⅱ) on kaolinite, and even around pH 5～6 the adsorption percentage of copper (Ⅱ) increased from ca. 50% to ca. 65% in the presence of humic acids. As the high Al/Si dissolution ratio of kaolinite and the low dissociation extent of negative ligand of humic acids at pH<4 were not favorable for humic acid adsorption, a decrease in the adsorption percentage of humic acid on kaolinite surface was observed. However, in comparison with kaolinite, the adsorption percentage of copper on humic_kaolinite complexes increased obviously to some extent. The enhancement mechanism of copper adsorption on kaolinite surface was the formation of ternary complexes of Al—HA—Cu (B_type) at the edge of kaolinite, unlike the effects of the traditionally-considered factors such as pH, electrolyte concentration and initial ion concentration. As simultaneous deprotonation of the groups of both the humic acid and the kaolinite edge at pH>7 was intensified, and electrostatic repulsion among the groups reduced the adsorption percentage of humic acid on kaolinite, a decrease in copper (Ⅱ) adsorption on kaolinite occurred in the presence of humic acids. Nevertheless, at pH＞7 the precipitation of humic-copper (Ⅱ) complexes and Cu(OH)2 probably took place, and the apparent sorption percentage of copper (Ⅱ) on kaolinite only changed insignificantly.