Mesenchymal stem cells (MSCs) from bone marrow are believed to be an ideal cell source for cardiomyoplasty; however, cellular electrophysiology is not understood. The present study was designed to investigate ion channels in undifferentiated rat MSCs. It was found that three types of outward currents were present in rat MSCs, including a small portion of Ca2+-activated K+ channel (IKCa) sensitive to inhibition by iberiotoxin and/or clotromazole, a delayed rectifier K+ current (IKDR), and a transient outward K+ current (Ito). In addition, tetrodotoxin (TTX)-sensitive sodium current (INa.TTX) and nifedipine-sensitive L-type Ca2+ current (ICa.L) were found in a small population of rat MSCs. Moreover, reverse transcription-polymerase chain reaction revealed the molecular evidence of mRNA for the functional ionic currents, including Slo and KCNN4 for IKCa; Kv1.4 for Ito; Kv1.2 and Kv2.1 for IKDR; SCN2a1 for INa.TTX; and CCHL2a for ICa.L. These results demonstrate for the first time that multiple functional ion channel currents (i.e., IKCa, Ito, IKDR, INa.TTX, and ICa.L) are present in rat MSCs from bone marrow; however, physiological roles of these ion channels remain to be studied.