Aqueous biopolymer mixtures are characterized by a very low interfacial tension, challenging most of the existing methods to measure this quantity. Here we apply a fast and accurate rheo-optical methodology, based on small angle light scattering (SALS), to obtain the interfacial tension of an aqueous gelatin-dextran biopolymer mixture. Two methods are compared. The first one is based on the analysis of the SALS patterns during fibril break-up under quiescent conditions, the second uses the anisotropy of the SALS patterns during relaxation after steady state shearing. The resulting values of the interfacial tension, obtained by the two methods, are in good agreement. In addition, the effect of temperature on the interfacial tension has been studied. (C) 2002 Elsevier Science Ltd. All rights reserved.