The facile processes were developed for synthesizing vanadium dioxide (VO2) by pyrolyzing ammonium metavanadate (NH4VO3) in nitrogen (N2) flow and by thermal reduction of vanadium pentoxide (V2O5) in ammonia gas. X-ray diffraction (XRD), scanning electron microscopy (SEM) and differential scanning calorimetry (DSC) were applied to analyzing the product VO2. The experimental results indicated that VO2 microcrystal particles were successfully synthesized from both NH4VO3 and V2O5. From NH4VO3 the product VO2 presents two kinds of micro morphologies, torispherical and pentagonal prism. The phase transition mainly takes place at 337.8K and 341.8K. The average enthalpy of phase transition is 28.82 J/g. From V2O5 the product VO2 presents rhombohedral. The phase transition temperature is approximately 342.6K and the enthalpy of phase transition is 44.90 J/g.