Bone marrow mesenchymal stem cells (MSCs) are used as a cell source for cardiomyoplasty; however, the cellular electrophysiological properties are not fully understood. The present study was to investigate the functional ionic channels in undifferentiated mouse bone marrow MSCs using whole-cell patch voltage clamp technique, reverse transcript polymerase chain reaction (RT-PCR), and Western immunoblotting analysis. It was found that three types of ionic currents were present in mouse MSCs, including a Ca²⁺-activated K⁺ current (I_KCa), an inwardly rectifying K⁺ current (I_Kir), and a chloride current (I_Cl). I_Kir was inhibited by Ba²⁺, I_KCa was activated by the Ca²⁺ ionophore A23187 and inhibited by the intermediate conductance I_KCa channel blocker clotrimazole. I_Cl was activated by hypo-osmotic (0.8T) conditions, and inhibited by the chloride channel blockers DIDS and NPPB. The corresponding ion channel genes and proteins, KCa3.1 for I_KCa, Kir2.1 for I_Kir, and Clcn3 for I_Cl, were confirmed by RT-PCR and western immunoblotting analysis in mouse MSCs. These results demonstrate that three types of functional ion channel currents (i.e., I_Kir, I_KCa, and I_Cl) are present in mouse bone marrow MSCs.