Improving foam stability is an important issue in foam fractionation of proteins from their aqueous solutions with low foam properties. In this work, enhancing protein self association at the gas-liquid interface by sodium citrate (Na-citrate), instead of adding surfactants, was used to improve the stability of protein foams. Using bovine serum albumin (BSA) as a model protein, the role of Na-citrate in enhancing self-association of BSA at the gas-liquid interface was studied at the molecular level. Then, the role of the enhanced protein self-association in intensifying foam fractionation of BSA was studied. The results show that by weakening electrostatic repulsion between the BSA molecules and unfolding their structures, Na-citrate induced the formation of 12 and 18 BSA aggregates at the gas-liquid interface. The enhanced protein self-association effectively increased the interfacial adsorption of BSA and improved the foam stability. At BSA concentration 50 mg/L, the recovery percentage of BSA with 30 mmol/L Na-citrate increased by 4 folds while its enrichment ratio just decreased by 11.5%, compared to those without Na-citrate. The results give a clear understanding of the role of protein self-association in foam fractionation of proteins. (C) 2016 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.