LaMnO3-based perovskite oxides are typical functional materials applicable to various devices for its chemistry and physics properties. The conventional method solid-state reaction method has some drawbacks of high reaction temperature, large particle size and limited degree of chemical homogeneity. So, an easy, low cost and environmental method of synthesizing fine and homogenous powders of LaMnO3 is required. This paper discusses the synthesis of LaMnO3 via a mechanochemical activated process. The mixtures of La2O3 and Mn2O3 were used as starting powders. The specific surface of starting materials was measured by BET method. A planetary ball mill was used to grind the starting mixtures. During the grinding process, XRD analysis was employed to make clear the phase changes, and BET analysis was used to test the specific surface changes. After being grinded for different time, the mixtures were annealed at different temperatures. After this, the phase identification of mixtures was conducted by XRD. At the same time, a pre-mixing of starting materials with ethanol as solvent by normal ball-milling for 8 hrs was proceeded to obtain homogeneous mixture and improve the efficiency of grinding. All obtained LaMnO3 powders via the mechanochemical activated process were characterized by SEM imaging. Finally, an optimized powder processing was proposed.