Mesoporous MCM-41 and Fe loaded MCM-41 (Fe/MCM-41), which were successfully prepared by a hydrothermal method and a dipping method respectively, were applied as heterogeneous catalysts for ozonation of p-chlorobenzoic acid (ρ-CBA) in aqueous solution. MCM-41 and Fe/MCM-41 were characterized by XRD, FT-IR and diffuse reflectance UV-vis (DR-UV-vis) techniques. The presence of either MCM-41 or Fe/MCM-41 improves p-CBA and total organic carbon (TOC) removal efficiency compared to ozonation alone. Under the experimental condition, TOC removal rate of Fe/MCM-41/O3 process is over 63.5% at 60 min oxidation time, 44.5% using MCM-41 as catalyst, only 37.7% with ozonation alone. The presence of /erf-butanol (TBA) in the Fe/MCM-41/ O3 process indicated that the oxidation mechanism of ρ-CBA occurs via OH in the liquid bulk. And Fe/MCM-41 is a promising catalyst.