Dodecanethiol-protected gold nanoparticles were deposited onto fumed SiO2 (Cab-O-Sil) via colloidal deposition. The catalyst was treated with a strongly oxidative KMnO4 or K2MnO4 solution. Low-temperature conversion in catalytic CO oxidation increased dramatically following the oxidative treatment and subsequent thermal activation at 300 degrees C to burn off residual organic species. On the other hand, the treatment with Fenton's reagent did not lead to any positive effect. The influences of the average sizes of pre-synthesized gold particles (1.8, 2.1, 3.9, 9.9 nm) and the choice of different supports (SiO2, TiO2, C) were investigated, and relevant characterization using TG/DTG, XRD, TEM, EDX, and HAADF was conducted. The catalyst stability as a function of time on stream was also surveyed. This work establishes the beneficial effect of treating dodecanethiol-capped gold catalysts by KMnO4 or K2MnO4.