Objective To observe the effect of epigallocatechin gallate (EGCG) on the spatial learning memory deficit in amyloid procursor protein(APP)/presenilin-1(PS1) double transgenic mice, synaptic ultrastructure and expression of neural cell adhesion molecule in hippocampal CA1 region.   Methods Eight weeks old male APP/PS1 double transgenic mice were selected as Alzheimer’s disease (AD) model and divided into the model group, the EGCG group and the donepezil hydrochloride group, 12 in each group.Besides，normal mice of the same brood (with no transgene) were recruited as a normal group (n=12). Related indices were detected after 6 months continuous gastrogavage. The spatial learning-memory deficit of APP/PS1 double transgenic mice was detected by Morris water maze test.The synaptic ultrastructure of hippocampal CA1 region was observed by transmission electron microscopy. The expression levels of neural cell adhesion molecule (NCAM) and polysialyltranseferase α2,8-polysialic acid (ST8Sia Ⅱ) protein in hippocampal CA1 region of APP/PS1 transgenic mice were detected by immunofluorescence and Western blotting.   Results Compared with the normal group, the mean value of escape latency in the model group was extended, and compared with the model group, the mean value of escape latency in the EGCG group and donepezil hydrochloride group were increased (P<0.05). The result  of electron microscope showed that the changes of synaptic interface curvature of EGCG group and donepezil hydrochloride group were not obvious. Compared with the model group, the width of the synaptic gap becomes narrower and the thickness of the postsynaptic compact were increases (P<0.05). Immunofluorescence showed that the expression of NCAM and ST8Sia Ⅱ proteins in the hippocampus CA1 region was expressed in the cytoplasm of neurons, the expressions of NCAM and ST8Sia Ⅱ in hippocampal CA1 region were significantly increased in EGCG group and donepezil hydrochloride group (P<0.05). Their contents also showed higher levels of expression in Western blotting (P<0.05).  Conclusion EGCG shows improvement on the spatial learning-memory deficit in APP/PS1 double transgenic mice，which may be associated with affecting the synaptic structure of hippocampus and improving the expressions of neural cell adhesion molecule.