The utilization of copper-impregnated HZSM-5 (Cu/HZSM-5) zeolites as catalysts for the gas-phase catalytic oxidation of benzene was attempted. The major products were phenol, carbon dioxide, and carbon monoxide. The Si/Al ratio in the HZSM-5 support of the Cu/HZSM-5 catalyst influenced both the yield of and the selectivity for phenol, both of which increased with a decrease in the Si/Al atomic ratio of the HZSM-5 support with constant Cu loading. The amount of carbon monoxide uptake of the prereduced Cu/HZSM-5 catalysts decreased with a decrease in the Si/Al atomic ratio of the HZSM-5 support of the Cu/HZSM-5 catalyst. The yield of phenol over the Cu/HZSM-5 catalyst increased, along with both the yield Of CO2 and CO, by adding water vapor in the reaction system. The oxygen species adsorbed on the Cu/HZSM-5 catalyst were suggested to be responsible for the formation of phenol, based on the results of the transition response experiment. The amount of the isolated Cu2+ species with square-pyramidal configuration on the Cu/HZSM-5 catalyst estimated from the ESR observation was found to have a correlation with the yield of phenol.