Objective:To investigate the mechanism of learning and memory impairment of apolipoprotein E -/- ( ApoE-/-) mice after transient global cerebral ischemia by diffusion tensor imaging (DTI) and magnetic resonance spectroscopy (MRS). Methods:Ten-week-old C57BL/6(WT) mice and ApoE-/- mice were randomly divided into WT sham-operated group ( n=8), WT 7 d group ( n=12) and WT 30 d group ( n=12), and ApoE-/- sham-operated ( n=8), ApoE-/- 7 d group ( n=12) and ApoE-/- 30 d group ( n=12). The mice in the WT 7 d group, WT 30 d group, ApoE-/- 7 d group, and ApoE-/- 30 d group received bilateral common carotid artery ischemia-reperfusion injury, while mice in the WT sham-operated group and ApoE sham-operated group only stripped the blood vessels without ligation. On the 7 th and 30 th d of modeling, Morrris water maze test was employed to detect the learning and memory abilities of these mice; DTI was used to detect the fractional anisotropy (FA) values in the bilateral hippocampus of mice, and MRS was used to detect the contents of choline complex (Cho) and N-acetylaspartate (NAA) in the bilateral hippocampus of mice. Results:(1) On 2 nd, 3 rd, and 4 th d of water maze experiment, the escape latency of mice in ApoE-/- 7 d group was significantly prolonged as compared with that in the ApoE-/- sham-operated group and WT 7 d group ( P<0.05); since the 3 rd d of water maze experiment, the escape latency of mice in ApoE-/- 30 d group was significantly prolonged as compared with that in WT 30 d group ( P<0.05). The number of times crossing platform in ApoE-/- 7 d group was significantly smaller than that in WT 7 d group, and the residence time in the third quadrant was significantly shorter ( P<0.05); the number of times crossing platform in ApoE-/- 30 d group were significantly smaller as compared with that in the WT 30 d group, and the residence time in the third quadrant was significantly shortened ( P<0.05). (2) DTI results showed that there was no significant difference in bilateral hippocampal FA values between ApoE-/- 7 d group and WT 7 d group ( P>0.05); the bilateral hippocampal FA values of mice in the ApoE-/- 30 d group were statistically lower than those in WT 30 d group ( P<0.05). (3) MRS results showed that the relative contents of hippocampal Cho and NAA in the ApoE-/- 7 d group were significantly lower than those in the WT 7 d group, and the relative contents of hippocampal Cho and NAA in the ApoE-/- 30 d group were significantly lower than those in the WT 30 d group ( P<0.05). Conclusion:ApoE-/- mice have poor learning and memory abilities after transient global cerebral ischemic injury, whose mechanism is closely related to the damage of hippocampal white matter fibers and abnormal metabolism of nerve cells.