Objective To research the effect of Benzo[a]pyrene（BaP）on morphological changes of hippocampal neurons in rats that exposed to BaP through observing the morphological changes of hippocampus tissues BaP by light microscope and electron microscope.Methods 50 SD rats were randomly divided into control group（n=10）and experimental group（n=40）.After being exposed to BaP

the rats in experimental group were divided into 5groups according to the time they have been executed（1hafter exposure group

1dafter exposure group

2dafter exposure group

3dafter exposure group

5dafter exposure group）

and each group of 8SD rats.BaP was injected into rats of experimental group via caudal vein

similarly the rats of control group were injected with normal saline of same dosage as experimental group.After the BaP exposure

the hippocampus tissues of rats were obtained for observation by light microscope and electron microscope at specific points in time.Results Compared to the control group

rats in experimental group after BaP exposure were easily to show abnormal symptoms of being surprised

excited

irritated

insensitive and slow in response.Through the observation of light microscope

in the comparison of 2groups

there was no significant difference between their quantities and forms of hippocampal neuron.And electron microscope results of each rat′s hippocampus showed that there were concentrated degeneration of soma

plasmolysis

expansion of rough endoplasmic reticulum

and mitochondria swelling

etc.Conclusion Acute BaP exposure could damage the hippocampal neurons of rats.