Rheology of aqueous casein-guar gum mixtures is very sensitive to their phase state. In the one phase region, the flow behavior and viscoelastisity of the mixtures remained qualitatively similar to those of the corresponding guar solutions; however, a slight increase in the viscosity and in the storage and loss moduli was observed which points to some kind of molecular interaction between the two macromolecules in the mixtures. As soon as the binodal was crossed, the systems exibited thixotropy. Very complex shear rate and shear time effects were observed. Viscosity and moduli dropped to values noticeably lower than the values of the corresponding continuous phases when the latter were the guar-enriched phases. Phase inversion was accurately detected through the changes in the rheological behavior. To understand the rheological properties of the mixtures in the two phase regions one probably has to take into account, besides elongation of the droplets of the dispersed phase under shear, the possibility that the mechanical energy input could shift the position of the system in the phase diagram.