A NiO-Fe2O3-Na2O catalyst achieved an extremely high space-time yield (STY) of phenol, while maintaining a high phenol selectivity, as compared with that of a conventional CuO catalyst for the vapor phase oxidation of benzoic acid. The addition of Na2O to NiO-Fe2O3 catalyst was found to be very effective in increasing the STY of phenol, while maintaining a high phenol selectivity. The effect of temperature, oxygen ratio, H2O ratio, and space velocity on the catalyst performance were examined in order to optimize the phenol selectivity and STY of phenol. The reaction route for phenol formation over the Na2O-promoted NiO-Fe2O3 catalyst was also speculated upon by considering the deactivation of the catalyst.