In this study, we report the physical properties of sub-stoichiometric Molybdenum trioxide (MoO3-x) thin films synthesized by thermal evaporation technique for photocatalytic application. MoO3-x thin films were deposited on glass and Fluorine doped Tin Oxide (FTO) coated glass substrates with different thicknesses (100 - 650 nm). Structure analysis by X-ray diffraction and field emission scanning electron microscope confirm the amorphous structure of MoO3-x films deposited on FTO and glass substrates. The optical analysis by UV-Vis–near-infrared spectrophotometer showed that the optical band gap does not depend on the substrate type and takes values in the range from 3.6 to 3.31 eV. The Corrosion measurements for MoO3-x films deposited on FTO coated glass substrates were performed using an electrochemical potentiostat in a neutral medium of NaCl solution. The corrosion studies demonstrate that the as deposited MoO3-x film of thickness 650 nm exhibits the highest corrosion resistivity compared with other thicknesses. The methylene blue (MB) was employed as a representative dye pollutant to evaluate the photocatalytic activity of the current samples. The results show that the film thickness and substrate type play an important role in the enhancement of the photocatalytic properties of MoO3-x films. We found that the deposited films on glass decompose MB more than the films deposited on FTO. In addition, the as deposited MoO3-x film of thickness 100 nm exhibit the highest photocatalytic activity as compared with the other deposited films.