This paper presents a study of the phase evolution induced by mechanical milling in mixtures Ln(2)O(3):TiO2 (Ln=Gd, Dy) with two different stoichiometries, 1:1 and 1:2. Starting from oxides, pyrochlores Ln(2)Ti(2)O(7) and the hexagonal beta-Ln(2)TiO(5) forms were obtained at room temperature by milling the initial mixtures in a planetary ball mill using zirconia balls and mortars. Mechanically activated chemical reactions involve titanium oxide and the monoclinic B-Ln(2)O(3), obtained this one during the initial stages of the milling process, from the starting highly symmetric cubic form, C-Ln(2)O(3). Differential thermal analysis of the just milled powders showed in every case, the presence of an exothermic event at temperatures close to 800 degrees C which is thought to be due to some order disorder event. (c) 2005 Elsevier B.V. All rights reserved.