The catalytic effects and mechanisms of the ozone/carbon nanotube (O₃/CNT) process using para-chlorobenzoic acid (pCBA) were evaluated. To use pCBA as an O₃-resistant OH• probe compound in a pure water system at pH 7, an adequate amount of scavenger was needed. During the O₃/CNT process, a synergetic catalytic effect by OH• generation on the CNT surface could be evaluated in the condition of excess tert-butyl alcohol (TBA) concentration. The OH• radicals were generated and existed on both the bulk phase and CNT surface. The OH-ct values of the CNT surface and bulk phase in the O₃/CNT process for 10 min were 2.1×10^-5 and 2.5×10^-5 μM·s, respectively. In modifying CNT evaluation, the catalytic effects were the most apparent in the following order: CNT treated with acid then heat (CNT-T), original untreated CNT (CNT-O), and CNT treated with an acid (CNT-A).