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In the present study, FeOOH/γ-Al2O3catalyst was first introduced into dielectric barrier discharge (DBD) plasma-catalysis system for toluene degradation, and its catalytic performance and mechanism were studied. It was found that the toluene degradation efficiency, energy yield (EY), and COxselectivity were significantly improved in the plasma-FeOOH/γ-Al2O3system by comparison to the plasma-only process. The ozone concentration detected in this study decreased significantly in plasma-FeOOH/γ-Al2O3system, which could be concluded that the ozone catalytic process played an important role in the plasma-FeOOH/γ-Al2O3system for toluene degradation. The toluene and intermediates adsorbed on the surface FeOOH catalysts could react with O* from O3decomposition and Oadsderived from oxygen vacancies, which was conducive to an improved degradation and mineralization performance. Besides, the transformation of O3to ·OH on FeOOH surface was considered as one of the main mechanisms for enhancing toluene degradation when the relative humidity of the background gas was increased from 30% to 50%. The key process parameters, including specific energy input (SEI), catalyst loading, and oxygen content of the background gas, were optimized by response surface methodology (RSM) integrated Box-Behnken design (BBD). The results showed that oxygen content of the background gas was the most significant factor affecting the degradation efficiency of toluene, while energy yield was mainly determined by SEI. The possible toluene degradation pathways in plasma-FeOOH/γ-Al2O3system were proposed according to the identification of intermediates using GC-MS.