OBJECTIVE The purpose of this study was to investigate the effect of hyperbaric oxygen (HBO) therapy on de novo bone formation during periosteal distraction (PD). METHODS Periosteal distraction was performed in 24 mature male New Zealand rabbits using a custom-designed device placed on the lateral surface of the mandibular corpus. Twelve rabbits (group H) were given adjunctive HBO treatment, whereas 12 rabbits (group N) were kept in a normal environment (normobaric oxygen). After a 7-day latency period, the same distraction protocol was applied to both groups. However, the rabbits in group H were treated with pure oxygen at 2.4 atm absolute for 25 times. Both groups were further divided into 2 subgroups and killed after consolidation periods of 4 and 8 weeks. Photodensitometric and histologic analyses were performed to evaluate the newly formed bone. RESULTS There was no significant difference between the 4-week consolidated HBO group and the 8-week consolidated normobaric oxygen subgroup (P = 0.229). Moreover, there was better bone formation in the 8-week HBO group than in the 8-week control group. CONCLUSIONS The results of this study indicate that PD with HBO could be used to increase the quality and the quantity of the bone newly formed by PD.