Decomposition of methanol over Cu-Ni/SiO₂ catalysts which were prepared with various Cu/Ni ratios was carried out and the roles of copper were in- vestigated by comparing the reaction results with those obtained from a nickel -only catalyst. Although the surface composition of copper was much higher than that of nickel, the overall catalytic characteristics such as the activation energy, selectivity and activity were similar to those of the nickel-only cata- lyst. Thus it is concluded that the decomposition of methanol takes place mainly on the nickel sites. Incorporation of copper reduces the number of adjacent nickel-site pairs, resulting in decrease of the TOF(turnover frequen- cy) of methanol decomposition and inhibition of the methane formation. As the Cu/Ni ratio increased, the formation of methane became more inhibited while no obvious trend was observed for the activation energy and the TOF. The reaction order was almost independent of the Cu/Ni ratio and also remained constant with the partial pressure of methanol, contrary to the case for the nickel-only catalyst; this is considered to be another effect of copper.