A novel microfluidic mixer based on the modulation of /spl zeta/-potential is proposed and demonstrated successfully. In contrast to previous micromixer work from other groups, this micromixer does not need complex three-dimensional serpentine microstructure or external pumps to generate chaotic advection pulsatile flow. The mathematical models for /spl zeta/-potential variation, induced pressure distribution, volumetric flow rate, and the velocity profile in a rectangular cross-section microchannel is derived and show the mixing effect of varying /spl zeta/-potential. Numerical simulation results utilizing CFD-ACE+ indicate the good mixing efficiency for our micromixer design with asymmetric herringbone electrodes and periodic voltage control. The microfabrication process for our electrokinetic micromixer has been developed successfully. Experimental results demonstrate a great mixing enhancement via our microfluidic mixer. Our electrokinetic micromixer design can induce complex flow fields easily to enhance the mixing effect by appropriate modulations of the /spl zeta/-potential. The work reported here considers for the first time temporal/spatial /spl zeta/-potential modulation for microfluidic mixer applications.