Photoelectrochemical (PEC) solar-fuel conversion is a promising approach to provide clean and storable fuel (hydrogen) directly from sunlight and water. Direct photo-electrolysis in PEC water splitting is a more elegant and potentially cheaper approach because it consists of simultaneous function of both light harvesting and electrolysis in a single device. WO₃ is an indirect band gap semiconductor (E_g ≈ 2.6–2.8 eV) capable of capturing approximately 12% of the solar spectrum. Due to its band gap, WO₃ is considered as more suitable material than TiO₂ for photoelectrochemical water splitting application. WO₃ photoanode has a theoretical maximum conversion efficiency of solar energy into H₂ of about 4.8% in photoelectrochemical water-splitting device. Band gap engineering for tungsten oxide (WO₃) is necessary to narrow its band gap and increase light absorption ability for improved photoelectrochemical (PEC) properties. Doping WO₃ with foreign atoms is very efficient strategy to tailor its band gap through modification in the band edge positions. In this work, we have demonstrated a facile hydrothermal method for the fabrication of band gap tuned WO₃ thin films for PEC water splitting applications. The physical properties of synthesized Mo doped WO₃ thin films were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), transmission electron microscopy (TEM), energy-dispersive X-ray analysis (EDS), UV-Vis absorption spectra and X-ray photoelectron spectroscopy (XPS). Systematic studies were performed to investigate the presence of Mo in the WO₃ thin films. The characterization result shows that doping of Mo into WO₃ results significant change in the morphology without changing the crystal structure. Uniform distribution of Mo was observed in WO₃ by elemental mapping and the approximate quantity of Mo dopant was confirmed using EDS analysis in TEM. The incorporation of Mo into WO₃ reduces the band gap of WO₃ and increases its light absorption ability. Above all, From XPS valence band edge analysis, we confirm that, substitution Mo into WO₃ leads to the shift in the conduction band minimum downwards without any significant change in valence band maximum with respect to fermi level (Figure a). Mo doped WO₃ electrodes exhibited higher photocurrent than the un-doped samples under simulated 1.5 AM sunlight without an added water oxidation catalyst (Figure b). Furthermore, in comparison to un-doped WO₃ electrodes, Mo doped electrodes exhibit higher IPCE values and showed slight red shift in the onset wavelength (Figure c). Impedance measurements show that Mo doping improves electrical conductivity. The procedure proposed here, demonstrates a simple and systematic approach for the fabrication of band gap tailored WO₃ photoanodes by Mo doping for efficient PEC water splitting. Overall, this work is expected to have a relevant influence on future research toward fabricating doped WO₃ thin films for improving the PEC.