We previously reported that genetically obese mice exhibit innate airway hyperresponsiveness (AHR) and enhanced ozone (O₃)-induced pulmonary inflammation. Such genetic deficiencies in mice are rare in humans, and may not be representative of human obesity. Thus, the purpose of this study was to determine the pulmonary phenotype of mice with diet-induced obesity (DIO), which more closely mimics the cause of human obesity. Therefore, wildtype C57BL/6 mice were reared from the time of weaning until at least 30 weeks of age on diets in which either 10 or 60% of the calories are derived from fat in the form of lard. Body mass was approximately 40% greater in mice fed 60 versus 10% fat diets. Baseline airway responsiveness to intravenous methacholine, measured by forced oscillation, was greater in mice fed 60 versus 10% fat diets. We also examined lung permeability and inflammation after exposure to room air or O₃ (2 ppm for 3 h), an asthma trigger. Four hours after the exposure ended, O₃-induced increases in bronchoalveolar lavage fluid protein, IL-6, KC, MIP-2, IP-10, and eotaxin were greater in mice fed 60 versus 10% fat diets. Innate AHR and augmented responses to O₃ were not observed in mice raised from weaning until 20-22 weeks of age on a 60% fat diet. These results indicate that mice with DIO exhibit innate AHR and enhanced O₃-induced pulmonary inflammation, similar to genetically obese mice. However, mice with DIO must remain obese for an extended period of time before this pulmonary phenotype is observed.