Yield stress of concentrated mixed suspensions is of considerable importance in processing fine particle suspensions, for example, in colloidal processing of ceramics such as alumina-zirconia bodies, and in management and disposal of wet wastes, slurries, sludges, slimes, etc. We have measured yield stress of flocculated alumina-zirconia mixed suspensions over a wide range of solid loading and composition. Powders employed in these experiments, namely, alumina A16, alumina SR and zirconia Unitec, differ significantly in their fineness and size distribution. A model is presented for shear yield stress of mixed flocculated suspensions by integrating two recent results pertaining to the theology of concentrated suspensions. One, a structural model of shear yield stress for flocculated, single-component suspensions which explicitly incorporates the effects of solid loading and size distribution of the powder. Two, an empirical mixing rule for the effect of solid composition on yield stress of two component systems. The combined model is in good agreement with the experimental data. It could provide useful quantitative information on the role of solid loading, composition and particle size distribution on yield stress of mixed suspensions for an improved understanding of the processing of fine particulate fluids.