A well-crystallized mesoporous hydrous ruthenium dioxide (RuO_xH_y) with high surface area of 120 m² g⁻¹ and high electrochemical catalytic activity has been synthesized by a replicating route with the mesoporous silica (KIT-6) as hard template. The materials were characterized by means of thermo-gravimetric analysis (TG), X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM) and N₂ sorption. The electrocatalytic activity of the samples for methanol oxidation were investigated by cyclic voltammetry (CV) and linear scan voltammetry (LSV) techniques. A mixed gas of CO and O₂ was adopted to investigate the effect of gas treatment on the electrochemical activity of the samples. The results show that the electrocatalytic activity of the prepared mesoporous RuO_xH_y and 3 wt% Pt/mesoporous RuO_xH_y toward methanol oxidation was much enhanced after treatment with a mixed gas of CO and O₂. The enhanced electrochemical catalytic activity of the materials might be attributed to the structure activation during the gas treatment and the high surface area of RuO_xH_y matrix with mesoporous structure.