Objective To investigate the effect of hyperbaric oxygen（ HBO） preconditioning on isoflurane（ ISO）- induced cognitive impairment in middle-aged mice， and the effects of hyperbaric oxygen （HBO） pretreatment on the protein expression and mRNA levels of brain-derived neurotrophic factor（ BDNF） and glial cell-derived neurotrophic factor（ GDNF） in hippocampus. Methods A total of 32 male 8-month-old C57BL/6J mice were randomly divided into four groups by random number table with 8 in each group： sham group， HBO group， ISO group and HBO+ISO group. Mice in HBO group and ESPs+HBO group were put into hyperbaric oxygen chamber for 1 h（ 2.5 atmospheres， 100% O2）， while those in control group were intervened by atmospheric pressure（ simulating other processes and environmental conditions except pressure and oxygen concentration） for 1 h， which lasted for 5 days. On the third day after HBO or atmospheric air intervention， mice in each group were given water maze training for 3 days. 24 hours after the last water maze training， the cognitive impairment models were established by isoflurane inhalation anesthesia in ISO group and HBO+ISO group， while the other two groups inhaled control gas. After 24 hours， the cognitive function was detected by water maze， and the protein expression and mRNA levels of BDNF and GDNF in hippocampus of mice were detected by Western blot and real-time quantitative polymerase chain reaction（ qPCR）. Results （1） There was no significant difference in the total movement distance and average movement speed in water maze test among each group（ P＞0.05）； the relative time dwell time in target quatrant in the ISO group was（ 26.74±10.52）%， which was significantly lower than that in the sham group（ 48.33.74±9.21）%（ P ＜ 0.01）， while that in HBO+ISO group（ 39.06±8.38）% was significantly higher than that in ISO group（ P ＜ 0.05）.（ 2） The relative expression levels of BDNF（ 0.56±0.09） and GDNF（ 0.52±0.10） in hippocampus of ISO group were significantly lower than those in sham group and HBO+ISO group（ P＜0.01 or 0.05）（. 3） The relative mRNA levels of BDNF（ 0.51±0.08） and GDNF（ 0.25±0.09） in hippocampus of ISO group were also significantly lower than those in sham group and HBO+ISO group（ P＜ 0.01）.（ 4） There was no significant difference between sham group and HBO group in the above parameters（ P＞0.05）. Conclusions Hyperbaric oxygen preconditioning may improve isoflurane induced cognitive impairment by regulating the expression of BDNF and GDNF in hippocampus.