A new way of compatibilization of an aqueous phase-separated two-component biopolymer system based on physical interactions of the constituents with a third biopolymer (compatibilizer) was suggested. The rheological behavior and the changes in morphology of the compatibilized mixtures were studied using a two-phase water-casein-alginate system, with the droplet morphology as a model. The time-dependent evolution of the microstructure of the compatibilized casein-alginate emulsion was investigated by image analysis using optical microscopy. Addition of 0.04-1.5 wt% of dextran sulfate as compatibilizing molecule to the emulsion leads to a considerable increase in the compatibility of casein with alginate and to a dramatic increase in storage and loss moduli (G' and G"). Rheological differences could be correlated with differences in morphology, visible by optical microscopy.