Mesoporous molecular sieve MCM-41 and Cerium-loaded MCM-41 (Ce/MCM-41) were synthesized and used as heterogeneous catalysts for ozonation of p-chlorobenzoic acid (p-CBA) in aqueous solution. MCM-41 and Ce/MCM-41 were characterized by XRD, TEM, SEM, ICP-AES and N-2 adsorption-desorption techniques. The results showed that Ce/MCM-41 retained a highly ordered mesoporous structure and had a surface area of 953 m(2) g(-1). The presence of Ce/MCM-41 obviously improved the mineralization of p-CBA and the conversion rate of organic chlorine. The conversion rate of organic chlorine in Ce/MCM-41/O-3 process was 94% along with the degradation of p-CBA in the first 10 min (73.3% by O-3 alone and 78.6% by MCM-41/O-3), TOC removal efficiency by Ce/MCM-41/O-3 process was 94% at 60 mm (63% by MCM-41/O-3 and only 52% by O-3 alone), and the leaching of cerium was only 0.097 mg l(-1). The combination of Ce/MCM-41 and O-3 exhibited a significant synergetic effect. Both pH changes of aqueous solution and the presence of hydroxyl radical scavenger tert-butanol (TBA) proved that Ce/MCM-41 catalytic ozonation of p-CBA followed the HO center dot oxidation mechanism. The changes of ozone concentration indicated that the presence of Ce/MCM-41 could promote ozone decomposition into hydroxyl radical, and improve the utilization rate of ozone. Lewis acid sites and the hydroxyl group existing on the surface of catalyst were believed to be the initiator of ozone decomposition to generate HO center dot. (C) 2013 Elsevier B.V. All rights reserved.