Exposure to adverse early-life events is thought to be the risk factors for the development of psychiatric and altered cognitive function in adulthood. The purpose of this study was to investigate whether electroacupuncture (EA) treatment in young adult rat would improve impaired cognitive function and synaptic plasticity in adult rat with neonatal maternal separation (MS). Wistar rats were randomly divided into four groups: control group, MS group, MS with EA treatment (MS + EA) group, and MS with Sham-EA treatment (MS + Sham-EA) group. We evaluated the cognitive function by using Morris water maze and fear conditioning tests. Electrophysiology experiment used in vivo long-term potentiation (LTP) at Schaffer Collateral-CA1 synapses was detected to assess extent of synaptic plasticity. Repeated EA stimulation at Baihui (GV 20) and Yintang (GV 29) during postnatal 9 to 11 weeks was identified to significantly ameliorate poor performance in behavior tests and improve the impaired LTP induction detected at Schaffer Collateral-CA1 synapse in hippocampus. Collectively, the findings suggested that early-life stress due to MS may induce adult cognitive deficit associated with hippocampus, and EA in young adult demonstrated that its therapeutic efficacy may be via ameliorating deficit of hippocampal synaptic plasticity.