Objective   To investigate the function mechanism of hyperbaric oxygen（HBO) in neural repairation of neonatal rats after hypoxic-ischemic brain damage (HIBD).    Methods   Thirty 7-day-old rats were randomly divided into control group

HIBD group and HIBD+HBO group

with 10 rats in each. Bone morphogenetic protein-4（BMP-4）and nestin protein in the hippocampus were determined with immunohistochemical method while their messenger ribonucleic acid (mRNA) were determined with in situ hybridization. Apoptosis of nerve cells was determined with TUNEL.    Results   Expression of BMP-4 and nestin protein in the hippocampus was the highest in HIBD+HBO group while their expression in HIBD group was lower than that in control group. Expression of BMP-4 and nestin mRNA in the hippocampus was the highest in HIBD+HBO group while their expression in HIBD group was lower than that in control group. Apoptosis of neural cells in HIBD group was the highest among the 3 groups while apoptosis of neural cells in HIBD+HBO group was lower than that in HIBD group（P0.01）.    Conclusion   HBO plays a role in nerve reparation

probably by promoting expression of BMP-4 and nestin in the hippocampus and inhibiting apoptosis of neural cells.