Hyperbaric oxygen (HBO2) has effects of the biology of cytokines and other mediators of inflammation. HBO2 suppresses the production of stimulus-induced proinflammatory cytokines and the liberation of prostaglandins (PGs) and nitric oxygen (NO) and increases the heme oxygenase-1 (HO-1) level. In this article, we discussed the effects of HBO2 on cytokines, PGs, NO and HO-1 involved in inflammation, and the correlation between HBO2 and periodontitis.