The secondary ionization of lithium metal and lithium iodide by contact with an argon ECR plasma was studied. Lithium and argon ion densities in the lithium-argon mixture plasma were diagnosed by using double probes, a photospectrometer and a mass spectrometer. According to plasma diagnostics, the apparent ionization cross sections were ∼ 10 −16 m 2 for lithium metal and ∼ 10 −17 m 2 for lithium iodide. This ionization method produces a low-temperature plasma which would be appropriate for ion cyclotron resonance isotope separation.