Mercaptans are molecules with high volatility, responsible for unpleasant odours. They have a very low olfactory threshold, e.g. for CH3SH of ~0.39 ppbv. In this paper, copper oxide nanoparticles supported on graphene were synthesized for the removal of low-concentration CH3SH (5 ppm). That results show that the humidity has a significant impact on the elimination of odors. The adsorption ability grows at increasing conditions of relative humidity (RH). The adsorption capacity at RH = 80 % is 2 or 5 times higher than that shown at RH = 4 %. The surface of CuO nanoparticles is highly responsible for the formation of hydrated complexes that are effective in the acquisition of CH3SH.