Mixing is crucial yet challenging work in the laminar, low Reynolds number microfluidic devices. In this paper, a microchannel comprising a mixing unit embedded with geometric features is designed to enhance the mixing. Instead of complex spatial geometries and sample strategies, simple periodic geometric features are applied to decrease the required mixing distances. In computer simulations and experiments, geometric features in the mixing unit increase periodically and good mixing occurs after a 28-period mixing unit. (C) 2012 Elsevier B.V. All rights reserved.