Precursor of nanocrystalline LaMnO3 was synthesized by solid-state reaction at low heat using La(NO3)(3)center dot 6H(2)O, MnSO4 center dot H2O, and Na2CO3 center dot 10H(2)O as raw materials. XRD analysis showed that precursor was a mixture containing orthorhombic La-2(CO3)(3)center dot 8H(2)O and rhombohedral MnCO3. When the precursor was calcined at 800 degrees C for 2 h, pure phase LaMnO3 with rhombohedral structure was obtained. Magnetic characterization indicated that rhombohedral LaMnO3 behaved weak magnetic properties. The thermal process of the precursor experienced four steps, which involved the dehydration of crystallization water at first, and then decomposition of manganese carbonate into MnO2, and decomposition of La-2(CO3)(3) and MnO2 together into La2O2CO3 and Mn2O3, and lastly reaction of monoclinic La2O2CO3 with Mn2O3 and formation of rhombohedral LaMnO3. Based on the Kissinger equation, the value of the activation energy associated with the formation of rhombohedral LaMnO3 was determined to be 260 kJ mol(-1). The value of the Avrami exponent, n, was equal to 1.68, which suggested that crystallization process of LaMnO3 was the random nucleation and growth of nuclei reaction. (C) 2012 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.