Mechanochemical synthesis of zinc ferrite, ZnFe2O4, was attempted from a powder mixture of iron (III) oxide, alpha-Fe2O3 and zinc (II) oxide, ZnO. Nanocrystalline zinc ferrite, ZnFe2O4 powders were successfully synthesized only by milling for 30 hours. The X-ray diffraction spectrum of the as-milled powders (without heating) showed twelve ZnFe2O4 peaks and four weak peaks of coexisting unreacted Fe2O3. The crystallite size of the mechanochemicallysynthesized ZnFe2O4 was 26.3 nm. Evidence of the ZnFe2O4 formation was absent for the powders milled for 10 and 20 hours; milling lowered the crystallinity of the starting materials. Heating after milling enhanced the formation of ZnFe2O4, the crystal growth of ZnFe2O4 and the unreacted starting materials. The unreacted starting materials decreased their amounts by heating at higher temperatures.