The effect of polymorphism of Al2O3 on sintering and grain growth of magnesia aluminate spinel was studied. γ - Al2O3 and α - Al2O3 were mixed with MgO according to the stoichiometric MA ratio, respectively, and pressed into billets with a 20mm diameter and 15mm height, and then were sintered at temperature from 1250ºC to 1400ºC in air atmosphere. Bulk density, apparent porosity and grain size were measured. The results indicated that the grain size of MA with γ-Al2O3 is larger than the grain size of MA with α - Al2O3. This is because the activation energy of grain growth of magnesia aluminate spinel prepared by γ-Al2O3 is lower than that by α -Al2O3, the former is 159KJ/mol and the latter is 217KJ/mol.