Abstract: Based on the conditions of 7S forming fibril,the emulsifying and foaming properties of soy protein 7S and11S( including acidic and basic subunits) was investigated under prolonged heat treatment at low p H. The results showed that the foaming properties of different soy protein components were significantly improved( p < 0.05),while the emulsification was not sigificantly regular changed even the emulsion stability was reduced by heating treatment at low p H. There were no relationships between the fibrillar aggregates and modified properties.Compared with the heating treatment at p H7.0,the surface hydrophobicities of soy protein 7S and 11 S were significantly increased under heating treatment at low p H,and the special structure with high surface hydrophobicities was benefit for improving foaming properties of soy protein. Then,the surface hydrophobicities and foaming properties of 7S and 11 S were improved significantly after prolonged heat treatment at low p H.