Purposefully improving the performances of copper-based oxides for Hg-0 oxidation was beset with difficulties due to their vagueness of Hg-0 oxidation mechanism. In this study, Hg-0 oxidation mechanism over CuO/TiO2 was deeply investigated by Hg balance, kinetics, and transient reaction. HgO adsorbed on CuO/TiO2 scarcely reacted with gaseous HCl to form HgCl2, so the Mars-Maessen mechanism scarcely contributed to Hg-0 oxidation over CuO/TiO2. The reaction order of He oxidation over CuO/TiO2 at 300-400 degrees C with respect to the gaseous Hg-0 concentration was much less than 1, so neither the Deacon mechanism nor the Eley- Rideal mechanism predominated over Hg-0 oxidation over CuO/TiO2. As the contributions of other three mechanisms to Hg-0 oxidation over CuO/TiO2 were all ruled out, Hg-0 oxidation over CuO/TiO2 mainly followed the Langmuir-Hinshelwood mechanism, which can reasonably explain all the experimental phenomena of Hg-0 oxidation over CuO/TiO2.