Fe2O3 powders with different crystallite sizes prepared by heating FeOOH at various temperatures were ground with La2O3 powder using a planetary ball mill to investigate the effect of crystallite size on mechanochemical synthesis of LaFeO3. Fe2O3 powder with smaller crystallite size obtained by heating at lower temperature reacts more easily with La2O3 than that with larger size. The mechanochemical reaction proceeds with an increase in grinding time. Specific surface area of the LaFeO3 powder synthesized has a large value of over 11 m(2)/g. The mechanochemical process can be also applied to synthesize other iron complex oxides with rare earth elements such as Pr, Nd and Sm.