Hippocampal-dependent learning and memory processes are associated with theta frequency rhythmic activity. Interneuron and pyramidal cell network interactions underlie this activity, but contributions of interneuron voltage-gated membrane conductances remain unclear. We show that interneurons at the CA1 lacunosum-moleculare (LM) and radiatum (RAD) junction (LM/RAD) display voltage-dependent subthreshold membrane potential oscillations (MPOs) generated by voltage-gated tetrodotoxin-sensitive Na+ and 4-aminopyridine (4-AP)-sensitive K+ currents. They also exhibit prominent 4-AP-sensitive A-type K+ currents, with gating properties showing activation at subthreshold membrane potentials. We found that LM/RAD cells are part of specific interneuron subpopulations expressing the K+ channel subunit Kv4.3 and their transfection with Kv4.3 small interfering RNA selectively impaired A-type K+ currents and MPOs. Thus, our findings reveal a novel function of Kv4.3-mediated A-type K+ currents in the generation of intrinsic MPOs in specific subpopulations of interneurons that may participate in hippocampal theta-related rhythmic activity.