Two different processes for synthesizing fine lanthanum cobalt oxide (LaCoO3) powder with an aid of mechanochemical treatment have been introduced in this paper. One is a direct synthesis process, which is to grind a mixture of La2O3 and Co2O3 powders using a high-energy mill such as a planetary ball mill. The grinding causes mechanical reaction between the two compounds, leading to synthesize LaCoO3 and the reaction is facilitated with an increase in milling time. The product powder (LaCoO3) agglomerates, so that its specific surface area (SSA) is about 3.5 m(2)/g. Another process is composed of three steps: the first step is to grind a mixture of LaCl3, CoCl2 and NaOH, stimulating a solid-state reaction to form La(OH)(3), Co(OH)(2) and NaCl. The second step is to calcine the ground mixture at 873 K to change the hydroxides into complex oxide (LaCoO3), and the final step is to wash out NaCl from the heated mixture. The product forms weak agglomerates, and its specific surface area is about 10 m(2)/g, which is much larger than that in the direct process. (C) 2004 Elsevier B.V. All rights reserved.