Ｏｂｊｅｃｔｉｖｅ　To evaluate the effects of sevoflurane by different inhalation time on cognitive function in aging rats.　Methods　A total of 40 SD rats (18?蛳month old, male) weighing (600±50) g were randomly divided into 5 groups (n=8): the normal control group (C group), and other groups receiving 3% sevoflurane for 0.5(S1 group), 1(S2 group), 2(S3 group), 4 h(S4 group), respectively. The Morris water maze was selected for all groups to evaluate hippocampal function the day after sevoflurane exposure. The expression of N-methyl-D-aspartate receptor type 2B(NR2B) in the hippocampus was measured by Western blot ting 15 min after Morris water maze.　Results　Compared with C group［（5.5±1.2）, （48.2±6.2） s］, platform crossing times and time spent in the platform quadrant were decreased obviously in S3 group［(3.8±1.0), (39.1±4.0) s］　and S4 group ［(1.9±1.0), (31.6±3.2) s］(P<0.05), respectively. Compared with S3 group, platform crossing times and time spent in the platform quadrant were decreased more significantly in S4 group(P<0.05). NR2B expression of S1 group (0.69±0.88) decreased significantly compared with C group(1.00), while no significant difference was seen in S2 group. Compared with C group, there was a significant increase in NR2B expression of S3 group(1.47±0.17) and S4 group(2.17±0.10).　Conclusions　Anesthesia with 3% sevoflurane for 2 h and 4 h can induce cognitive decline in aging rats. There was a positive correlation with inhalation time possibly through overexpression of NR2B in hippocampus of aging rats.