Depression is growingly recognized as a major public health problem. A large body of data supports the notion that alterations in oxygen (O₂) supply to the brain contribute to the pathophysiology of depression. We examined safety and efficacy parameters of chronic normobaric O₂ treatment (NO₂T) in naïve and stress-subjected "depressed" rats. Safety parameters – including hematological, biochemical, and respiratory – were tested in naïve rats. Other groups of rats were subjected to a stress protocol and then treated with NO₂T (40 % O₂) for four weeks. Post-stress rats underwent behavioral assessments and evaluations of brain inflammatory mediators and serotonin levels. We found that: i) NO₂T was associated with a high tolerability profile in naïve rats; ii) NO₂T produced a potent antidepressant-like effect as well as other positive behavioral outcomes in post-stress rats; and, iii) NO₂T decreased inflammatory components and kynurenine, and increased serotonin levels in the frontal cortex and hippocampus of post-stress rats. This study provides evidence for the efficacy and safety of NO₂T in a rodent model of depression, highlighting its potential as a novel antidepressant treatment. Further research is needed to explore long-term effects and underlying mechanisms.