This paper has x-rayed an approach to investigate the crystallite size of thermally deposited gold nanoparticles on a glass substrate. The mined and beneficiated gold sample was deposited on glass slide in Nano-38 thermal depositor after the substrate has been technically prepared. The crystallite size and profile fitting of the nanoparticles were determined by X-ray Diffractometer (XRD). The result showed that the average crystallite size of Au nanoparticles thermally deposited on glass slide was 14.4 ± 6.7 nm with lattice constants: a, b, c; 4.0789, 4.0789, and 4.0789 (Å) respectively. The TEM images have confirmed that high quality spherical Au NPs that were between 18 nm – 24 nm were successfully synthesized. The XRD has shown that the material of the gold nanoparticles is gold and crystalline in structure. Narrow size distribution and small monosize gold nanoparticles produced may proffer advantages for self-assembled monolayer formation and enhanced surface area.