Synaptic dysfunction induced by amyloid-beta protein (Aβ) has been shown to play a critical role in cognitive deficits of Alzheimer's disease (AD). Currently, however there is no clinical causative therapy for the disease. S14G-humanin (HNG) is best known for its strong neuroprotective ability against AD-related insults in vitro, and several in vivo studies have shown its effectiveness in ameliorating the cognitive impairment, but the precise mechanism of HNG on neuroprotection still remains to be elucidated. The present study examined the effects of HNG on Aβ-induced inhibition of hippocampal long-term potentiation (LTP) in mouse hippocampal slices. The results disclosed that soluble Aβ25–35 significantly inhibited the induction of early-phase LTP (E-LTP) and late-phase LTP (L-LTP) in the hippocampal CA1 region without affecting the basal synaptic transmission, while HNG significantly ameliorated such inhibition of E-LTP and L-LTP in a dose-dependent manner. In addition, the reduction of phosphorylated CREB trigged by Aβ25–35 was restored by HNG during L-LTP induction, possibly attributing to the improvement of the L-LTP inhibition. Collectively, our findings add to the evidence that soluble Aβ-induced LTP inhibition may represent an early pathological event of AD, and demonstrate for the first time that HNG may improve LTP inhibition by subneurotoxic concentration of soluble Aβ, suggesting that HNG may have therapeutic potential for Aβ-induced synaptic dysfunction closely associated with cognitive deficits in the early stage of AD.