Three-dimensional opal-VO2 photonic crystals were synthesized by the chemical bath deposition technique. The Bragg reflection spectra from the (111) planes of the crystals were measured as a function of the temperature in the range between 15 and 100°C. The thermal hysteresis loop of the reflection peak position due to the phase transition in VO2 filling the opal voids was observed. A theoretical model of the periodic layered medium was proposed to describe quantitatively the reflection spectra of opal-like structures. The values of the dielectric constants of the VO2 below and above the phase transition temperature have been estimated which give the best fit within the model considered.