Mesoporous WO 3 -TiO 2 composite films were prepared by a sol gel based two stage dip coating method and subsequent annealing at 450, 500 and 600°C. An organically modified silicate based templating strategy was adopted in order to obtain a mesoporous structure. The composite films were prepared on ITO coated glass substrates. The porosity, morphology, and microstructures of the resultant products were characterized by scanning electron microscopy, N 2 adsorption-desorption measurements, l-Raman spectroscopy and X-ray diffraction. Calcination of the films at 450, and 500°C resulted in mixed hexagonal (h) plus monoclinic phases, and pure monoclinic (m) phase of WO 3 , respectively. The degree of crystallization of TiO 2 present in these composite films was not evident. The composite films annealed at 600°C, however, consist of orthorhombic (o) WO 3 and anatase TiO 2 . It was found that the o-WO 3 phase was stabilized by nanocrystalline anatase TiO 2 . The thus obtained mesoporous WO 3 -TiO 2 composite films were dye sensitized and applied for the construction of photochromic devices. The device constructed using dye sensitized WO 3 -TiO 2 composite layer heat treated at 600°C showed an optical modulation of 51 % in the NIR region, whereas the devices based on the composite layers heat treated at 450, and 500°C showed only a moderate optical modulation of 24.9, and 38 %, respectively. This remarkable difference in the transmittance response is attributed to nanocrystalline anatase TiO 2 embedded in the orthorhombic WO 3 matrix of the WO 3 -TiO 2 composite layer annealed at 600°C.