Styrene is a typical volatile organic compound (VOC) emitted from various sources that is considered hazardous due to its toxicity and strong odor. Many technologies have been developed to control VOCs, including plasma, catalytic, and thermal oxidation. In this study, styrene, one of the typical VOCs, was decomposed by ozone (O3) in laboratory and on-site systems. In a laboratory reactor, the styrene conversion efficiency in the reaction was determined under different temperatures, inlet styrene concentrations, and [O3]/[styrene] mole ratios. The styrene conversion efficiency decreased as the reaction temperature increased and was higher at higher mole ratios. A complete conversion was obtained in the laboratory system at room temperature, and 58.3% styrene conversion efficiency was achieved in the on-site system.