VO2(B) was synthesized via a facile hydrothermal process using V2O5 and oxalic acid. The crystal structure and phase transition of VO2(B) during elevated temperatures in N2 were investigated by in situ X-ray diffraction (XRD). Meanwhile, the morphology and crystal structure of the samples obtained by annealing at different temperatures were characterized by Field Emission Scanning Electron Microscopy (FE-SEM) and XRD, respectively. The results show the as-synthesized nano platelet-like monoclinic VO2(B) irreversibly transforms into submicron and micron subsphaeroidal tetragonal VO2(R) between 430 and 700 oC. The as-obtained VO2(R) starts to decompose and form Magn閘i phases VnO2n?1 series compounds at 1000 oC, and totally transfers into a corundum V2O3 sintered block at ca. 1200 oC.