Vanadium dioxide (VO₂) thin films were prepared on c-sapphire substrates by using an easy sol–gel method and sequential vacuum annealing process. The effects of annealing time on the structure, morphology and phase transition properties were investigated. The results show that, with the extended annealing time from 1 h to 7 h, the films have transformed from V₂O₃ to V₃O₅, and then VO₂. The VO₂ thin films prepared with the annealing time of 4 h or 7 h display good phase transition property with the resistance change up to 3 orders of magnitude. Furthermore, the 7 h-sintered film has better growth orient, bigger grain size and lower phase transition temperature comparing with the 4 h-sintered film. It is suggested that, the prolonged annealing treatment will be in favor of the crystal film quality and enhance the related phase transition property for the solution-based VO₂ films. Based on the Raman results, we have discussed the possible reactions and evolution mechanisms during the VO₂ film preparation with different annealing time.