Diethyl phthalate (DEP) degradation by graphite supported metal oxide catalytic ozonation in aqueous solution was conducted. The activity and stability of graphite supported ZnO (ZnO/graphite) catalyst, the effects of preparation parameters and operational conditions on the activity of ZnO/graphite, and the mechanism of DEP degradation by ZnO/graphite catalytic ozonation were studied. ZnO/graphite has the highest activity on ozonation of DEP among the MnOx, FeOx, CrOx, CoOx, NiOx and ZnO supported on graphite catalysts, and it keeps excellent catalytic activity during reuse. ZnO/graphite catalyst prepared with 3.5% loading of zinc and calcined at 573 K in N2 atmosphere has the highest activity, and the rodlike ZnO nanoparticles are formed on the graphite surface. The ZnO/graphite catalyst dose, the ozone dose and the initial solution pH exert positive effect on ozonation of DEP. The presence of ZnO/graphite enhances the utilization efficiency of ozone from 52.1% (ozonation alone) to 72.1%, and reduces more than half of the apparent activation energy for ozonation of DEP. It is proposed that the DEP oxidation occurs both in bulk solution and on the surface of ZnO/graphite catalyst, and OH plays a key role in bulk solution.