Effective separation and condensation processes are essential for precise detection of circulating tumor cells in early diagnosis of cancer. In this study, we proposed a dielectrophoretic device with micro pillar electrodes as cell separator. Also, we simulated the spatio-temporal behavior of model cells on the basis of microfluidics and electrokinetics. The particle trajectory in a flow direction was changed by dielectrophoretic force generated between the pillars. This result suggests the tumor cells can be purified from real blood under adequate electrical condition.