Objective:To investigate the effects of chronic ethanol intake and withdrawal on the synaptic plasticity in dorsal striatum of rats. Methods:Rats were fed with ethanol for 10,20,30d and withdrawal 1,3,7d. Extracellular recording was used to test the changes of long-term potentiation(LTP) induced in slices of dorsal striatum and transmission electron microscope(TEM) was used to observe the changes of synaptic ultrastructure. Results:Chronic ethanol exposure suppressed the induction of LTP to different extents in dorsal striatum,with the strongest suppressive effects on LTP occurring in 10d ethanol treated rats compared with control group(P < 0.05).The depression was attenuated in 20d and 30d ethanol treated rats(P > 0.05) and notably,LTP was potentiated in withdrawl 7d rats(P < 0.05).In the synaptic ultrastructure of dorsomedial striatum,the length of synaptic active zone was longer in withdrawal 7d rats,while the width of synaptic cleft was narrower in 20d and 30d ethanol treated rats and the post synaptic density(PSD) was thinner in 30d ethanol treated rats than that of control(all above P < 0.05). Conclusion:Chronic ethanol treatment may result in the changes of the efficiency of synaptic transmission and the ability of synaptic connection in rat dorsal striatum.