The effect of CuO loading on CuO/MgO catalysts was investigated for liquid-phase oxidation of H2S to sulfur. CuO/MgO catalysts were prepared by impregnating MgO with aqueous copper nitrate solution. All of the catalysts were characterized by BET surface analyzer, X-ray diffraction (XRD), and temperature-programmed reduction (TPR). It was observed that the HZS removal capacity with respect to CuO loading increased up to 4 wt.%, and then decreased with further increase in CuO loading. CuO addition up to 4 wt.% increased the BET surface areas, but beyond that it was decreased. The XRD showed that well dispersed CuO particles could be present on CuO/MgO at less than 4 wt.% CuO loading. The crystallites of bulk CuO became evident on CuO/MgO with more than 6 wt.% CuO loading, which were confirmed by a XRD. TPR experiments showed that CuO/MgO catalysts with CuO loading above 6 wt.% consisted of two phases of a well-dispersed and crystalline CuO. It was suggested that Cu2+ in the well-dispersed copper oxide domain could be the active species in the wet oxidation of H2S.