Effect of single administration of Polygala tenuipolia was examined on short-term memory in step through test and the intensity of the immunoreactive c-Fos protein induced by oral administration of ethanol. The acquisition of memory was significantly reduced by ethanol, and ethanol amnesia was remarkably reversed following oral administration of Polygala tenuifolia. c-Fos protein in normal rat brain was highly expressed in order of thalamus, pariental cortex, hippocampus, hypothalamus, amygdaloid and cingulate cortex. The expression of Fos protein was remarkably suppressed by single administration of ethanol. The inhibitory effect of ethanol on expression of Fos protein was reversed by single administration of Polygara tenuipolia, especially tissues of limbic areas such as amygdala, parietal cortex and CA3 of hippocampus. These results suggested that the amelioration process of Polygala tenuipolia on ethanol amnesia seems to be involve the expression of c-Fos protein in partly.