Numerous studies have examined the impacts of ground level O₃ on plants that are important for human consumption, but native species that are important for wildlife have received less scrutiny. During May–August 2004 we examined the effects of O₃ on biomass production and nutritive quality of highbush blackberry (Rubus argutus Link), an important forage for white-tailed deer (Odocoileus virginianus Zimmerman) and other herbivorous mammals. Plants were fumigated in open-top chambers with three levels of O₃ in a randomized-block experiment with three replicates of each treatment. Our three experimental treatments were carbon-filtered air, characteristic of clean air quality; nonfiltered air, representative of air quality in Auburn, AL; and air with double (2×) the ambient concentration of O₃. Although biomass production was not influenced by O₃ exposure, nutritive quality of plants was associated negatively with O₃ concentration. Specifically, neutral detergent fiber was greater and relative feed value was less in plants exposed to elevated levels of O₃. Similarly, in vitro dry matter digestibility tended to be less in plants exposed to elevated O₃. Nutritive quality of regrowth vegetation followed a similar pattern, where neutral detergent fiber was greater and relative feed value was less in plants exposed to elevated levels of O₃. These data suggest that elevated levels of ground level O₃ could have implications for diet selection of herbivorous mammals.