Abstract: In order to efficiently purify HCN in waste gases by catalytic hydrolysis, Equivalent-Volumetric Impregnation method was employed to modify γ-Al₂O₃ for hydrolytic decomposition of HCN. The effects of various selected metallic ingredients and their loading capacities on the efficiency of hydrolytic decomposition of HCN were investigated. The results indicated that the catalytic activities of active ingredients followed the order:Cu>Cr>Fe>Zn>Ni>Co. For the best catalyst, Cu/γ-Al₂O₃, optimum loading capacity of Cu was determined to be 15.0%. In addition, the catalysis activity of Cu/γ-Al₂O₃ was found to be improved by loading 1.0% of Ni. The purification efficiencies of the Cu/Ni/γ-Al₂O₃ catalyst were above 91% within 6 hours under the condition of airspeed at 18,0 h^-1, and 16.6 mg/m³ of NH₃ in the tail gas could be detected. The results of characterization using X-ray Diffraction (XRD), Scanning Electron Microscope/Energy Dispersive Spectrometer (SEM/EDS) and N₂ Adsorption-Desorption isotherm (N₂-BET) indicated that CuO is the main active ingredient in the Cu/Ni/γ-Al₂O₃ catalyst. The pore volume of the catalyst modified with Cu and Ni decreased for blocking micropores and mesopores with diameters of 1.7-15.0 nm, leading to the decrease of the efficiency of catalytic hydrolysis. Mesopores with small diameters played a main role in the hydrolytic decomposition of HCN.