Exposure of brain tissues to transcranial magnetic stimulation may induce persistent changes in neuronal activity and thus may influence synaptic transmission. However, data on the modulation of synaptic transmission by magnetic stimulation in vitro is scarce. We studied the effect of high-frequency magnetic stimulation (HFMS) on synaptic function in the rat hippocampal slice in vitro. To this end, synaptic transmission was monitored by electrical stimulation of Schaffer collateral axons and simultaneous recording of CA1 field potentials. HFMS was delivered through a circular coil positioned closely above the slice and consisted of 10 trains of 20 pulses at 100 Hz with 1 s intervals (5 repetitions with 10 s intervals). The intensity of the magnetic stimulus was adjusted to 60–75 A/ms. After the application of HFMS, electrically evoked CA1 field potentials showed a significant and long-lasting enhancement of synaptic strength at the Schaffer collateral-CA1 synapse. This enhancement was prevented in the presence of the selective N-methyl-D-aspartate (NMDA) receptor blocker D-AP5 (50 mM). Moreover, long-term potentiation induced by electrical tetanic stimulation was significantly reduced in slices that were treated with HFMS. In summary, we suggest that HFMS can elicit a NMDA receptor-dependent long-lasting enhancement of synaptic transmission in the rat CA1 region in vitro. In addition, HFMS appears to constrain the propensity of a slice to exhibit tetanus-induced long-term potentiation.