Ozone is the most important phytotoxic air pollutant in the United States. and Asclepias spp. (milkweeds) are among the most ozone-sensitive plants. Ten milkweed species were exposed to ozone in chambers within a greenhouse during 2018 and 2019. Asclepias syriaca (Common Milkweed) developed the greatest level of ozone-induced leaf injury (“stipple”) in both studies. Asclepias viridis (Green Antelopehorn) and A. eriocarpa (Woolypod Milkweed) exhibited moderate levels of ozone-induced stipple. Asclepias latifolia (Broadleaf Milkweed), A. fascicularis (Mexican Whorled Milkweed), A. arenaria (Sand Milkweed), A. viridiflora (Green Comet Milkweed), A. cordifolia (Heartleaf Milkweed), A. asperula (Spider Milkweed), and A. labriformis (Utah Milkweed) were tolerant, showing minimal or no stipple following exposure to ozone. Results were entered into a master database, which now lists the relative ozone-sensitivity or resistance of 22 of 76 (29%) milkweed species.