Surface roughness has been considered as a passive means of enhancing species mixing in electroosmotic flow through microfluidic systems. It is highly desirable to Understand the snergetic effect of three-dimensional (3D) roughness and surface heterogeneity on the electrokinetic flow through, microchannels. In this Study, we developed a three-dimensional finite-volume-based numerical model to simulate electroosmotic transport in a slit microchannel (formed between two parallel plates) with numerous heterogeneous prismatic roughness elements arranged symmetrically and asymmetrically oil the microchannel walls. We consider that all 3D prismatic rough elements have the same surface charge or zeta potential, the substrate (the microchannel Wall) surface has a different zeta potential. The results Showed that the rough, channel's geometry and the electroosinotic mobility ratio of the roughness elements surface to that of the Substrate, epsilon(mu), have a dramatic influence on the induced on the induced-pressure field, the electroosinotic flow patterns, and the electroosinotic flow rate in the heterogeneous rough, microchannels. The associated sample-species transport presents a tidal-wave-like concentration field at the intersection between four neighboring rough elements under low epsilon(mu), values and has a concentration field similar to that of the smooth channels under high epsilon(mu) values. (C) 2004 Elsevier Inc. All rights reserved.