Reactions of ZnO and TiO2 (anatase and rutile) in different mole ratios induced by high-energy ball milling were studied by X-ray diffraction. It was found that three main reactions could involve during high-energy ball milling: (1) (4 - X)ZnO + (2 + Y) TiO2 (anatase or rutile) --> Zn4-xTi2+YO8; (2) ZnO + TiO2 (rutile) --> ZnTiO3, and (3) TiO2 (anatase) --> TiO2 (II) --> TiO2 (rutile). Cubic Zn4-xTi2+YO8 nanocrystals with an average crystal size of about 15 nm can be prepared by high-energy ball milling, which could be an attractive process to fabricate material in industrial scale. No decomposition of ZnTiO3 into Zn2TiO4 and rutile was detected during milling. Anatase shows higher reaction activity than rutile and favours the formation of Zn4-xTi2+YO8 while rutile favours the formation of ZnTiO3. During the anatase-to-rutile transformation a transient metastable phase, TiO2 (II) which is a high-pressure phase of TiO2, is detected. (C) 2004 Kluwer Academic Publishers.