Both in situ high-energy X-ray diffraction and in situ X-ray absorption spectroscopy were used to investigate the structural evolution of materials during the solid-state synthesis of Li2MnO3. Combing X-ray absorption spectroscopy and factor analysis techniques, we were able to capture the spectrum and evolution of an intermediate phase (MnO2) that could not be detected by the diffraction technique. Meanwhile, the X-ray diffraction data clearly showed the anisotropic crystallization of Li2MnO3 during sintering above 600 °C.