Hippocampal long-term potentiation (LTP) is strongly associated with the acquisition of spatial memory and is attenuated by ethanol. Recent studies have shown that the inhibitory potency of ethanol against n-methyl-d-aspartate (NMDA) receptor-mediated synaptic activity is enhanced in hippocampal slices taken from juvenile rats compared to those taken from adults. In addition, ethanol has been reported to impair spatial memory acquisition at lower doses in adolescent rats compared to adults. We therefore hypothesized that the suppression of hippocampal LTP by ethanol would be more potent in hippocampal slices taken from adolescent rats compared to those taken from adults. The potency of ethanol against NMDA receptor-mediated LTP was assessed in area CA1 of hippocampal slices taken from adolescent (30 days old) and adult (90 days old) rats. In slices from adolescent rats, theta-burst stimulus trains reliably induced robust LTP in the absence of ethanol, but when the stimulus trains were presented in the presence of either 10 mM or 30 mM ethanol, LTP induction was significantly suppressed relative to controls. In contrast, there was no effect of these ethanol concentrations on the induction of LTP in hippocampal slices from adult rats. These observations indicate that ethanol suppresses LTP in the adolescent hippocampus at concentrations that do not affect than it suppresses in the adult slices, suggesting a much greater sensitivity to ethanol in adolescence.