Joint action of heating and ultrasonic treatment on the real structure of alpha -Fe2O3, and the kinetics of the interaction between alpha -Fe2O3 and MgO held under ultrasonic treatment were studied. Investigations of features of alpha -Fe2O3 real structure changes and kinetic analysis of the reaction of magnesium ferrite formation have shown, that solid state processes in the system treated by ultrasound at high temperatures are controlled by the change of lattice defect concentration, caused by processes of thermal and ultrasonic annealing on the one hand and lattice defect formation on the other hand.