Adsorption isotherms of β-lactoglobulin (p-LG) and acetylated β-lactoglobulin (Ac-β-LG). at the alumina/water interface are compared at pH value in the range 3·7 to 9·0.The isotherms of both modified and unmodified β-LG show highly pH-dependent behaviour. Both proteins showed the highest adsorption at pH 5·1. The greatest contrast between β-LG and Ac-β-LG occurred at pH 3·7 and 4·2 where β-LG showed positive adsorption and Ac-β-LG showed highly negative adsorption at the alumina/water interface. Aggregation of proteins leads to higher adsorption at pH Above pH 5·1, adsorption decreased to almost zero for both β-LG and Ac-β-LG, but on further increasing the pH to 9·0, adsorption becomes positive again. These results were related to the aggregation / dissociation property of β-LG in the entire pH range.