In this research, ozone decomposition has been synthesized based on copper oxide (CuOx) with granular activated carbon (GAC) as a support catalyst, being used as ozone decomposer in effluent gas emissions of industries that use ozone. Therefore, catalysts were made as a mask filter to decompose ozone. CuOx,, was impregnated to the surface of GAC by using copper carbonate (CuCO3) as precursor and then calcined to release carbon dioxide with temperature of 300 degrees C for 1 hour. Size of activated carbon and loading percentage of copper oxide to the support were varied to get the optimum value. The quality of a catalyst such as pore diameter and surface area are characterized by BET, the cross-sectional surface of the catalyst and the catalyst elements composition are analyzed by X-ray spectroscopy (SEM-EDX) and X-Ray Fluorescence (XRF), while CuOx, composition and crystal phase are analysed by XRD. Mask filter, which contained catalysts for ozone decomposition, was tested using a fixed bed reactor at room temperature and atmospheric pressure. Results of the catalytic conversion were tested using iodometric method. Activated carbon with smallest diameter (60-100 mesh) and highest loading percentage (2 %-wt) showed the highest activity which the ozone conversion to oxygen reached 100%. Amount of CuOx, on the support also determine the efficiency of catalyst due to appropriate amount of CuOx, probably maintain the morphology and crystal phase of the catalyst.