The process of p-xylene (PX) catalytic oxidation to terephthalic acid (TA) was studied at 60-110°C and atmospheric pressure with cobalt acetate as catalyst, glacial acetic acid as solvent, and ozone-containing air as oxidant. Effects of catalyst, temperature, ozone concentration, reaction time, and bromide on PX conversion and product selectivity were investigated. Results showed that PX was oxidized with 76% conversion and 84% selectivity for TA at 80°C under 63.0 mg/l ozone concentration for 6 h at 0.8 l/min gas flow rate when the mole ratio of PX to cobalt acetate was 10:1. PX conversion and TA selectivity could reach 96% and 84% when the mole ratio of PX to KBr was 1.84:1. When cobalt acetate, ozone, and bromide were simultaneously used, an obvious synergistic effect on the PX oxidation reaction was noted. Increasing the temperature gradually weakened the effect because the decomposition rate of ozone was accelerated.