In this work, a model ternary system of zeolite NaY, kaolin (both from Aldrich(R)) and alumina (from Vetec(R)), was studied. True and bulk densities, powder and particle porosities, specific surface area, and sorption isotherms were determined for single solids and mixtures. Physical properties and sorption isotherms of mixtures were calculated from the mixing rule using mass and volume fractions of each solid in the mixture. Calculated and experimental values presented very good agreement for true density, specific surface area, and sorption isotherms. For bulk density and porosity, the mixing rule does not work well, since the mixtures do not follow the mass proportion due to the particle-particle interactions. Zeolite NaY presents isotherm type 1, while kaolin and alumina present isotherm type 11, all mixtures present the curves between those of the single solids. The results show that it is possible to use the mixing rule to evaluate some physical properties as well as the sorption isotherms of binary and ternary mixtures of solids. (C) 2003 Elsevier B.V. All rights reserved.