This paper presents the development of a novel dielectrophoresis (DEP)-activated cell sorter (DACS) that has 3D-asymmeritc microelectrodes. The DACS conventionally utilizes relative strength between the DEP and drag forces. While the conventional cell separators usually depend on different size of cells, the new system differentiates similarly-sized cells by the difference of the electrical properties among cells. It distinguished different types of cells by their differences in electrical properties, conductivity and permittivity. Thus, continuously varying DEP forces generated by the system enabled us to separate MCF10A cells (normal cells derived from human breast epithelium) and MCF7 cells (human breast cancer cells) that have similar sizes. Applying the newly-developed system to separate two different cells, it was possible to separate cancer cells among normal cells.