A kind of crystal precursor, (NH4)(5)[(VO)(6)(CO3)(4)(OH)(9)]. 10H(2)O, less than 12 x 40 mu m in dimensions was synthesized by reaction of vanadyl dichloride and ammonium hydrocarbonate in solution. The precursor microcrystals were fined to less than 10 mu m with mean size of about 4 mu m, by using organic solvents and surfactant in the process of the synthetical technique. Thermolysis of the precursor in a flow of nitrogen gas was investigated by TGA and DTA. The XRD powders patterns for the products from the thermolysis of the precursor show that the VO2 powder obtained at 350, 365, 380 and 410 degrees C for 30 min were a noncrystalline phase, a monoclinic one named as B phase, a mixed phase of the B and the usual monoclinic A phase, and the pure A phase, respectively. SEM micrographs of VO2 powders from the fined precursor demonstrated that the particle sizes of these fine powders were less than 2 mu m. DSC curve of the VO2 obtained at 450 degrees C for 30 min from the fined precursor showed that there was an endothermic phase transition at 71 degrees C.