It is essential to study the thermal dewetting behavior of as-deposited nano-films for large scale and high-throughput fabrication. We report here on the nucleation of Au nanostructures onto titanium dioxide (TiO_x) thin films surfaces, which occurred in consecutive steps. First, TiO_x thin films were grown on quartz substrates reactively by e-beam evaporator and then thermally annealed at different temperatures, starting from 300°C to 900°C. Subsequently, a nano-film of Au was deposited on the top of these TiO_x surfaces. The stacked Au / TiO_x samples were post-annealed using muffle furnace at a temperature of 600°C for 1 h, to study the thermal dewetting properties and the controlled growth of the different TiO_x morphologies on the formation of Au nanoparticles (NP) and their plasmonic response. Such dual-structures were characterized accordingly to probe their topological, morphological, structural, and optical properties, by means of x-ray photoelectron spectroscopy, scanning electron microscope, atomic force microscopy, and ultra-violet–visible–near infrared characterization techniques. The thermal dewetting properties were found to improve at high temperatures (>500 ° C), where the Au NP size distribution was found to follow a Gaussian pattern centered around 30 nm. The average surface roughness also increased significantly with respect to the TiO_x dewetting temperature, which is mainly attributed to the porosity of the films. Finally, the absorption peak for Au nanostructures has shown a localized surface plasmon resonance close to 520 nm, along with a broad shoulder peak with a strong tail thereby reflecting the wide distribution of the formed Au NP sizes.