Objective To investigate the effect of Schisandrin B ( Sch B) on ultrastructural damage to hippocampal synapsesinduced by chronic alcoholism. Methods Rats were intragastrically administered 56° Hongxing Erguotou continuously for 8 weeksand were then randomly divided into four groups. Rats in the low-, medium-, and high-dose Sch B groups were treated with Sch B by gavage once a day for 30 consecutive days, the dose of Sch B in each group was 10, 20, and 40 mg / kg, respectively. A blank control group consisted of five ratsadministereddistilled water intragastrically. The Morris water maze was used to test the learning and memory ability of rats in each group. Transmission electron microscopy was used to observe the ultrastructure of neurons in the hippocampal CA1 area of rats in each group and to determine the morphological parameters of synapse structure. Results In the Morris water maze, compared with the blank control group, the incubation period of the spatial probe test and their time to cross the platform in the alcoholism group were significantly different (P< 0.05). Compared with the alcoholism group, the incubation periods of the spatial probe test of the low-, medium-, and the high-dose Sch B groups were shortened, and their times to cross the platform were increased, with these Results beingsignificant for the high-dose Sch B group (P<0.05). The following Results were observed by transmission electron microscopy of hippocampal cells of alcoholism group rats: cellular edema, swollen cell nucleus, decreased numbers of organelles, obviously swelled mitochondria, severely swelled synaptosomes, widened synaptic space, uneven dense matter in the post-synaptic membrane and significantly decreased number of synapses (P<0. 05). Compared with the alcoholism group, neurons in the Sch B groups had abundant cytoplasm, increased numbers of organelles, reduced cell damage, reduced synaptosome swelling, and clearer synaptic gaps. Compared with the alcoholism group, all Sch B groups had significantly increased numbers of synapses with shortened synaptic gaps and thickened dense matter in the post - synaptic membrane ( P < 0. 05). Conclusions Sch B can improve the synaptic plasticity of rat hippocampal CA1 neurons by changing their ultrastructure, thereby improving the learning and memory ability of rats with chronic alcoholism.