In this work, the microstructure of mechanically activated Fe2O3-Li2CO3-ZnO mixture for the lithium-zinc ferrites production was studied using the Shiner, Emmett, Teller and laser diffraction methods as well as X-ray diffraction and scanning electron microscopy analyses. The reactivity of reagent mixture was investigated by thermogravimetric and calorimetric analyses. The ball milling was performed in a AGO-2S high energy planetary ball mill with a vial rotation speed of 2220 rpm using steel grinding balls. The milling times were 0, 5, 15, 30 or 60 min. It was shown that the composition of mixture changes during the ball milling, which consists in decreasing the alpha-Fe3O4 concentration and increasing the Fe3O4 spinel phase, while the Li2CO3 and ZnO concentrations remain unchanged. It was found that the milling leads to decrease in the average particle size of the reagents and simultaneously formation of large size agglomerates with denser structure and well-interlinked particles. It was established that observed changes in microstructure and phase composition lead to an increase in the reactivity of the Fe2O3-Li2CO3-ZnO system and the acceleration of the chemical reaction between reagents.