Objective to investigate the long-term effects of sevoflurane given by different concentration and time course on cognitive function and expression of hippocampus BDNF in neonatal rats。Methods SD rats at seven-day-old were randomly divided into 4 groups。Rats only inhaled oxygen as control (group C) or inhaled sevoflurane at 5.1% for 1.3h（group S），at 3.4% for 2h（group M）and at 1.7% for 4h（group L）．Each group has 20 rats。Open field test and novel obiect recognition test were used to assess the cognitive function of the rats at 28-day-old。Then these rats were killed and measurede the expressions of BDNF and BDNFmRNA using immuno-histochemistry and RT-PCR in hippocampus respectively．Results ① In all tests，there was no significant change between group S and group C（P>0.05）. ② Group M didn’t not exhibit significant difference in comparison with group C in every item of the open field test。In the novel obiect recognition test，the percentage of exploring time on new object of group M in 24th hour was 63.4%，which showed significantly lower than controls 69.8%（P<0.05）. The average optic density of BDNF（0.229±0.021)and the relative value of BDNFmRNA（0.775±0.024）of hippocampus of group M were both lower than (0.0251±0.020) and (0.799±0.023) of control C respectivly（P<0.05）.③ No matter the tests of cognitive function or expressions of BDNF and BDNFmRNA ，each index of group L was worse than group C and group M（P<0.05）。Conclusion sevoflurane can induce forward cognitive decline in neonate rat ，that may be because of decreasing the expression of BDNF in hippocampus．The time of inhaleing sevoflurane was an important reason。