Gold (Au) nanoparticles of sizes in the range of 2–4nm dispersed on ordered mesoporous silica were prepared via a one-pot synthesis route in the presence of organosilane mercapto-propyl-trimethoxysilane (MPTMS). MPTMS was found to play a dual role: one was to coordinate the Au precursor (AuCl₄^-) via its thiol ligands and the other one was to form covalent bonds with the silica matrix. The interaction of the Au species with MPTMS was studied using real-time ultraviolet–visible spectroscopy and X-ray photoelectron spectroscopy techniques. The formation of Au (I)–thiolate complexes in the synthesis gel was identified and found to play a crucial role in the dispersion of the final Au nanoparticles on the support. The Au nanoparticles dispersed on the mesoporous silica exhibited high catalytic activity and selectivity in solvent-free selective oxidation of cyclohexane using molecular oxygen.