Aim: This study aimed to evaluate the effect of hyperbaric oxygen therapy sessions on the levels of IgA. materials and methods: Eight patients were selected from the outpatient maxillofacial clinic with Class I acquired maxillary defects. The patients were randomly divided into two equal groups for whom will receive hyperbaric oxygen therapy. Group I: Patients with maxillary defects received hyperbaric oxygen therapy sessions. (HBOT) Prosthesis construction started 1 month after surgery. Group II: Patients with maxillary defect but didn't receive hyperbaric oxygen sessions. (NHBOT). Prosthesis construction 3 months after surgery. Conventionally processed and cured heat-cured PMMA obturators were constructed for both groups. For measuring IgA levels in saliva ELISA test was used. Saliva samples were collected immediately before the denture was delivered to the patient, one month and three months following insertion. Results: For group HBOT, The mean values recorded for the Salivary IgA were 75.390±12.699, 80.100±11.438, and 81.650±11.799 (mg/dL) immediately, after 1 month, and after 3 months respectively. Regarding group NHBOT, The mean values recorded for the Salivary IgA were 83.65±11.739, 93.55±12.043, and 95.05±11.413 (mg/dL) immediately, after 1 month, and after 3 months respectively. Conclusion: HBOT improved the tissue response to inflammatory conditions, however, the healing effects of hyperbaric oxygen therapy can last up to 12 months. If, and therefore when the maintenance phase of treatment is reached needed treatment one or two days per week may be required.