The addition reaction between the compacted powders of zinc oxide and aluminium oxide was studied. Both the reactants of different particles sizes were mixed in 1 - 1 molar ratio and compacted. Three particle sizes (ZnO <2 μm, Al2O3 < 18 μm, 84 μm) and four compaction pressures, 288 kgf/cm2, 576 kgf/cm2, 876 kgf/cm2 and 1152 kgf/cm2, were used for the studies. Conversions were measured at 800°, 900°, 1000° and 1100°C from 5 minutes to 5 hours. The reaction rate changed to a constant value after an initial phase boundary process. The mole percentage conversions increased with decrease in particle size of aluminium oxide, the increase in compaction pressure corresponding to a decrease in the initial porosity of the compact. It was also observed that the final porosity of the compact increased with increase in reaction temperature. The diffusion controlled model, Valensi-Carter model, was used to calculate the reaction rate constant equivalent. The activation energy was calculated to be 26.3-57.1 kcal/g.mole and 21.3-56.1 kcal/g.mole for the two particle sizes of aluminium oxide and for the temperature range of 800-1100°C. © 1975.