Progressively increasing ozone (O) concentrations pose a potential threat to the value of marigold (Tagetes erecta Linn.), a plant widely used in urban landscaping. The response of marigold to elevated O has been reported earlier, but the mechanisms underlying the O effect have not been clearly elucidated. In the present study, we exposed marigold "Moonsong Deep Orange" plants to elevated O, including ambient non-filtered air (NF) plus 60 ppb (NF+60) and 120 ppb (NF+120) O, to assess visible injury and the possible physiological consequences of this pollutant. Yellow lesions appeared after 4 days under NF+120 treatment and 12 days under NF+60 treatment, with 85.6% and 36.8% of the leaves being injured at harvest time, respectively. Compared with NF, NF+60 inhibited leaf photosynthesis, stem-diameter growth, and biomass production significantly, while the parameters were decreased more by NF+120. Although the stomatal conductance decreased under elevated O exposure, the O flux into leaves increased by 28.0-104.8% under NF+60 treatment and 57.5-145.6% under NF+120 treatment. The total ascorbic acid (ASA) content increased due to elevated O exposure, while the reduced ASA content did not, resulting in a decreased ratio of reduced to total ASA. A lower level of jasmonic acid (JA) was observed under elevated O exposure. In conclusion, the impacts of elevated O on marigold plants may be ascribed to increased O flux into leaves and reduced protective capacity of leaves to convert oxidized to reduced ASA and synthesize endogenous JA.