In this study, a high separation ratio micro-fluidic cell sorting by dielectrophoretic (DEP) force is presented. Resent development of iPS cell technology has promoted the possibility of regenerative therapy. In technologies of genetic cell processing requires purification of specific target cells by cell sorter. Most prevailing system for cell separation is the flow cytometry (FCM), which has been developed for research purpose. In spite of the high performance in separation ratio, it takes rather high cost in one operation. For clinical use, a device contacting biological specimen must be disposable to prevent cross infection. A low cost micro-fluidic cell sorter, using DEP force, can be fabricated by photolithography technique. However, sorting rate of existing DEP cell sorter is far lower than that of FCM because of the limitation of applicable voltage in aqueous fluid. To circumvent the problem and raise the DEP force, implementation of field gradient dependence was investigated. The design of flow channel was deiced to make high gradient at the separation point, and enhance the DEP force. Distribution of the electric field was proved to have a peak intensity at the entrance of separation channel by numerical calculated of Finite Element Method. DEP separation of 2μm diameter latex beads at the rate of 3.0mm/sec, 6 times large than that of our previous system, was demonstrated. © 2012 The Institute of Electrical Engineers of Japan.