We have compared the behavior of ovotransferrin at the air-solution interface in the presence of a monovalention (acetate), or a divalent ion (citrate), the latter being known to induce conformational changesof this protein upon interaction with its iron-binding sites. We have characterised the adsorption layer atthe air–water interface in terms of homogeneity, surface concentration excess and rheological propertiesat pH 4.0. Besides we have investigated the bulk conformation in the presence of the two anions. In thepresence of citrate only, interfacial layers display well-defined domains of higher overall surface concentrationsuggesting multilayers adsorption. Citrate also induces higher helical content and stabilizes theprotein against thermal denaturation. Hence we propose that these changes are involved in the propensityof ovotransferrin to self-assemble at the air–water interface resulting in thick and heterogeneousinterfacial layer.