Studies on the mechanism and kinetics of the reactions taking place in the solid state without mass change, involved in the synthesis of Fe4V2Mo3O20 have been made using X-ray diffraction (XRD) and infrared spectroscopy methods. The XRD study was carried out in a high temperature X-ray attachment. The mechanism of the synthesis process is discussed. The reaction rate constants and apparent activation energies for the distinguishable stages of the synthesis have been calculated, basing on the Erofeev model.