Manipulation of micro-sized particles and biological cells using dielectrophoresis (DEP) is an emerging technique in MEMS and nano technology[3]. This paper presents an exact solution of dielectrophoretic motion of a polarized particle in the vicinity of interdigitated bar electrodes fabricated on planar insulating surfaces which have been widely employed in conjunction with hydrodynamic forces and gravity to separate particles in field flow fractionation device[5]. We solved the electric field using exact mixed boundary conditions on the electrode plane. DEP forces exerted on a spherical particle are calculated and particle levitation is studied. Besides the levitation force, the particle will also experience a lateral force which causes particles clustering at certain locations above the electrode plane depending on the geometry of electrode array. Comparison is made with previous approximate solutions and numerical results.