Ozone is the most oxidative air pollutant and considered as an abiotic stress which harm to vegetation and crop. Similarly, biological stressor such as plant pathogen could cause severe damage to crops. Combination effects from both stresses will potentially lead to economic loss. Basically, plants will response to both abiotic stress and pathogenic stressor by generate antioxidants and phytoalexins. The concentration of these chemical indicate stress level in plant and also defence system response. This research is aimed to investigate the combination effects of ozone and Xanthomonas oryzae pv. oryzae on antioxidants and phytoalexins in rice (Oryza sativa L. cv. KDML 105). In this study, 45-day-old rice plants were used. Ozone was elevated at concentrations of 100, 200 and 300 ppb in the fumigating chambers for 12 hours. Xanthomonas oryzae pv. oryzae which caused bacterial blight disease in rice was selected as plant pathogen. Combining effects of ozone and Xanthomonas oryzae pv. oryzae were examined using ozone at a concentration of 100 ppb and Xanthomonas oryzae pv. oryzae 1x10 8 cells/ml inoculation. The experimental design was a completely randomized design with 2×2 factorials treatment and three replications required. Temperature, relative humidity and light intensity in fumigating chambers were controlled. The results of the combining effects showed the amount of antioxidants and phytoalexins were higher than those in single treatment. The experimental data indicated that the combining effects will result in more stress in rice. This suggests that, in rice plantation area with experience of ozone episode, pathogenic resistance rice strain should be considered to reduce combining effects.