The past few years, have witnessed a rapid increase in the application of microfluidic devices to chemical and biological analyses. These devices offer significant advantages over their traditional counterparts, including reduced reagent consumption, a more rapid analysis and a significant improvement in performance. Species mixing is a fundamentally important aspect of these devices since it is this mixing which generates the biochemical reactions necessary for their successful operation. Many microfluidic applications require the mixing of reagents, but efficient mixing in these laminar (i.e., low Reynolds number) systems are typically difficult. Instead of using complex geometries and/or relatively long channels, an electric field is applied to drive flow mixing in microchannels. Generally, the fluid is driven by the application of an external periodic AC electric field. However, the chaotic AC electric filed is never used to drive flow mixing in microchannels. Chaotic behavior is a very interesting nonlinear effect. In some physical systems, chaos is a beneficial feature as it enhances mixing in chemical reactions. This paper presents a numerical investigation of electrokinetically-driven flow mixing in microchannels with chaotic electric field. The simulation results show that the application of a chaotic external field enables a reduction in the mixing channel length and a high degree of mixing efficiency. It is shown that a mixing performance as high as 90% can be achieved by chaotic external electric field.