Mechanochemical synthesis of zinc ferrite (ZnFe2O4) from a powder mixture of zinc oxide (ZnO) and hematite (alpha -Fe2O3) by room temperature grinding using a planetary ball mill was investigated. The grinding enables us to obtain the amorphous mixture of the starting materials. Most of ZnO reacts with alpha -Fe2O3 to convert into insoluble amorphous zinc and iron compounds within 2h-grinding. Prolonged grinding enhances the crystallization of ZnFe2O4 from the amorphous compounds. ZnFe2O4 crystallized by the grinding for 3 h or more consists of nanocrystalline particles with high specific surface area.