The synthesis and structural properties of the layered oxide Li2MnO3 have been studied in details. It represents a key for a better understanding of the complex structural evolutions pointed out in the materials like Li(Li,Ni,Mn,CO)O-2 when they are used as positive electrode materials in lithium-ion batteries. Li2MnO3 samples were prepared either via coprecipitation or via a two step solid state reaction followed by different annealing treatments. Using X-ray and electron diffraction in combination with diffraction data simulations, we show that in function of the synthesis conditions, Li2MnO3 is obtained with various degrees of disorder, along the c monoclinic direction, in the stacking of the ordered Li1/3Mn2/3 sheets within the cfc oxygen packing. We show that this disorder decreases when the synthesis temperature increases but the synthesis of a material free of stacking faults is not possible with these synthesis routes. Finally, the similarities between the evolutions pointed out in Li2MnO3 due to the synthesis conditions and those previously observed in the materials like Li(Li,Ni,Mn,Co)O-2 related to the evolution of the cations distribution in the slabs are underlined. (C) 2009 Elsevier B.V. All rights reserved.