The present paper deals with the surface properties of some iron oxides by means of the equilibrium of iron oxides with 0.01N NH₄Cl solution.The results showed that surface charge of iron oxide was closely related with the pH.Positive charge of iron oxides (represented by Cl^- ion adsorbed) was significantly negatively correlated with the pH,but negafive charge (represented by NH₄⁺ ion adsorbed) was positively correlated with the pH.For synthetic iron oxides,the zero point of charge (ZPC) obtained when the adsorption capacity of counterions was equal to zero approximated that obtained from the potentiometric titration.Basic property of surface hydroxyl of iron oxide showed buffering effect on the H⁺ ions in acid NH₄Cl solution.