Gas-phase VOCs decomposition generally produces intermediates and causes secondary air pollution. To avoid this issue, we proposed a novel method for a typical gaseous VOC (toluene) degradation via catalytic activation of peroxymonosulfate (PMS) in the liquid phase. Herein, activated carbon supported monodispersed Co3O4 nanoparticles (Co3O4/AC) were prepared via a facile deposition method. It is highly efficient in PMS activation for toluene degradation due to the presence of Co-OH+ species and well dispersed Co3O4 on Co3O4/AC. A toluene removal efficiency of nearly 90% was maintained during the reaction, and few gaseous intermediates were discharged. Sulfate radical (SO4 center dot-) and hydroxyl radical (HO center dot) derived from PMS activation played different roles during toluene oxidation and mineralization. Electron spin resonance (EPR) suggested that the generation of plentiful SO4 center dot- resulted in the superior toluene degradation, and the presence of HO center dot can improve carbon mineralization. Radical quenching tests further confirmed that SO4 center dot- played a dominant role for toluene degradation, whereas the absence of HO center dot inhibited the carbon mineralization. The toluene degradation pathway in the Co3O4/AC-PMS system was proposed based on the intermediates identified by GC-MS.