Mixtures of Al2O3 and (MgCO3)(4) . Mg(OH)(2) . 5H(2)O, mechanically activated by intense grinding in a laboratory vibrating mill for up to 120 min, were additionally heat treated from 800 to 1250 degrees C, It was shown that more intense particle size reduction of the crystallites of basic MgCO3 from 39 to 13 nm took place during activation, while the Al2O3 crystallites became finer from 32 to 23 nm. The BET specific surface area of ground spinel mixtures increases up to 30 min of activation and decreases thereafter. With prolonged activation time the temperature of reaction termination drops after the same isothermal heating time. The beneficial effect of the mechanical activation of spinel mixtures on the development of the chemical reaction is due to both the particle size reduction of the reactants and the partial decomposition of basic MgCO3. The positive influence of intense grinding on the reaction product yield is more pronounced at lower temperatures.