The adsorption of chloride ions by three variable charge soils and four constant charge soils of China were determined in different concentrations of co-existing SO₄^2- and accompanying Na⁺, K⁺, NHNH₄⁺, Mg²⁺, Ba²⁺ and Al^₃+, respect ively. The results indicated that the amount of Cl^- adsorbed by soils in different electrolyte solutions decreased in the order AlCl₃ > BaCl₂ and MgCl₂ > KCl and NH₄Cl> NaCl. However, the difference of Cl^- adsorption among electrolyte solutions was more significant in variable charge soils. In the same electrolyte solution, the amount of Cl^- adsorbed by different soils decreased in the order latersol> red earth> red latersol> yellow brown earth> brown earth, dark brown earth and black soil, which agreed with the order of posit ive surface charge of these soils. For variable charge soils, within the range of 0.5 to 5 mmol L^-1 of Cl^- added, the adsorption can be described by the Langmuir equation sat isfactorily, and the adsorpt ion energy parameter (K) calculated from the equation was similar in magnitude when different cations co-existed. The pH of the equilibrium solution increased and the amount of Cl^- adsorbed by variable charge soils decreased significantly with increasing concentration of SO₄^2- co-existed. However, there was some difference in Cl^- adsorption by constant charge soils in the presence of SO₄^2- when compared with Cl^- adsorption by variable charge soils in the same condit ion. It suggested that the negative surface charge of variable charge soils increased with increasing concentration of SO₄^2- co-existed, but the SO₄^2- co-existed did not influence the negative surface charges of constant charge soils remarkably. The results obtained in this work imply that for variable charge soils, co-adsorption (simultaneously adsorption) and ion-pair adsorption of Cl^- with cations might be involved except electrostatic adsorpt ion when accompanied by univalent cat ions and bivalent or trivalent cat ions respectively. For constant charge soils, only co-adsorpt ion of Cl^- with cations might occur except electrostatic adsorption.