Recently, studies of selective separation of cells using dielectrophoresis (DEP) have been performed. However, these are not applied to a large scale separation because the separation speed was low. For the problem of the DEP separation, a DEP force is effectively acted only when it is close to the electrode. However, a DEP filter would be one of the answers for a large scale separation. In this paper, we discussed optimization of electrode geometries and arrangement of the DEP filter by using the finite element method (FEM) analysis in order to improve the separation efficiency. A DEP filter electrode using fine wire has a circular cross section, and in this case it became clear that the value of partial derivativeE(2)/partial derivativey was influenced by the diameter, and the optimum diameter was 0.6 times the electrode gap. Also we discussed for various electrode geometries such as circular, square, diamond, and equilateral triangle electrodes. It became clear that the optimal cross sectional geometry of the DEP filter electrode was square.