Allergy is a process involving immune and infl ammatory processes. Hyperbaric oxygen (HBO2) has been shown to modulate both the immune and infl ammatory responses. In the present study, we aimed to examine the role HBO2 therapy on eosinophil infi ltration and tissue injuries in an animal model of allergic lung infl ammation. C57BL/6 mice were sensitized via intraperitoneal injection with ovalbumin (OVA) on day 1, followed by repeated challenges with OVA inhalation on days 14-17. In control group, the OVA was replaced with vehicle. Animals were sacrifi ced on day 18. Bronchoalveolar lavage (BAL) was performed and the BAL fl uid was analyzed for its total and differential counts, protein concentration, and LDH activity. For HBO2 treatment, animals were exposed to 2 or 3 ATA of 100% O2 for 60-90 min for 4-5 days after initial OVA sensitization or during the inhalation challenge period. The OVA sensitization/challenge protocol effectively induced prominent alveolar eosinophil infi ltration and increases in BAL fl uid protein concentration and LDH activity. Although 2ATA HBO2 therapy did not reduce the pulmonary allergic infl ammation, 3ATA HBO2 effectively confer protection, as demonstrated by reduced esosinophils, LDH activity, and protein concentration in the BALF. This protection was associated with decreased level of serum IgE. Our results support that HBO2 therapy may have immune/infl ammation modulatory effects and deserves further exploration of its possible role in the management of allergic infl ammation.