Our goal is to develop a new automatic blood cell counter that can detect a small amount of leukemia cells in the blood of patients. In this paper, we examine whether living blood cells can be separated by employing the dielectrophoresis (DEP). Leukocytes were separated from erythrocytes by dielectrophoresis at 60MHz, 10Vpp. Then BALL-1 (Human B-cell Acute Lymphotropic Leukemia Cell Line) which is one kind of leukemia cells were separated from the normal leukocytes (Mononuclear) at 37KHz, 14Vpp. HL-60 (Human promyelocytic Leukemia cell line) cells were separated from the normal leukocytes (Granurocyte) at 45KHz, 14Vpp.