Experimental results are presented for the streaming potential of mixtures of silica and alumina. It is shown that the behavior of such intimate mixtures varies between that of the pure components. It is a function of the pore sizes and the surface potentials of the components. In an attempt to describe the relationship between the apparent streaming potential of a porous composite matrix and the microscopic streaming potentials of its component oxides, three models are discussed: the capillary tube model, the sandwhich cell model, and the network model. In the capillary tube model, the macroscopic potential is the averaged surface potential of its components oxides based on the surface area fractions. In the sandwhich cell, a component oxide which occupies a larger portion of the total surface area will be weighted more heavily in determining the macroscopic streaming potential.  A general equation is developed for streaming potentials in a composite network of pores. Results were obtained for two special cases, tubes in series and tubes in parallel. The two cases represent two extreme situations and yield entirely different results. In the former case the smaller pores have a dominant effect on the macroscopic streaming potential; while in the latter case, the larger pores dominate. Among the three models, the network model provided the best fit to experimental data.