The molybdenum oxide (MoO₃) and MoO₃@SiO₂ nanoparticles were successfully prepared using the chemical bath deposition (CBD) method. The photocatalytic activities of molybdenum oxide (MoO₃), SiO₂, and MoO₃@SiO₂ nanoparticles composite have shown a synergistic photocatalytic effect of SiO₂ combined with MoO₃. The first-order degradation rate constants for MoO₃, SiO₂, and MoO₃@SiO₂ nanocomposite were 10.3 × 10⁻³ min⁻¹, 15.1 × 10⁻³ min⁻¹, and 16.3 × 10⁻³ min⁻¹, respectively. The MoO₃@SiO₂ composite showed degradation efficiencies in the methylene blue solution close to 100% after 60 min of UV irradiation. The X-ray diffraction (XRD) showed that the MoO₃ powder has a hexagonal crystal structure and the silica is the tridymite type of SiO₂. The crystallite size was about 94 nm, 32 nm, and 125 nm for MoO₃, silica, and MoO₃@SiO₂, respectively, as calculated by the Scherrer equation. The scanning electron microscopy (SEM) images revealed that the MoO₃ powder consisted of a uniform hexagonal structure; the silica showed a rod-like micro-flake morphology and the MoO₃@SiO₂ composite had the appearance of coral-like structures.