Abstract: To study the effects of Polygala tenuigenin (TEN) on learning and synaptic configuration of hippocampal CA3 area in mice, 30 mice were divided randomly into the control group and TEN group. All mice were orally given TEN in dose of 4.50 gkg-1 or saline for 14 days, and then were trained. The mice were given drug or saline during training period. After 10 days training, seven mice in each group were measured for the synaptic density (Nv), the length of active zone, the width of synaptic cleft, the thickness of postsynaptic density (PSD) and the ratio of perforated synapses in hippocampal CA3. The results were: (1) TEN could improve the rates of correct response and decrease the numbers of trails to reach the learning criterion. (2) TEN could increase the synaptic density, the ratio of perforated synapses, the length of active zone and the PSD thickness, and reduce the width of synaptic clef. These results showed that TEN markedly improved the behavior-learning in mice, which may be related to improvememt of the plasticity of synaptic morphology.