A oscillating feedback microextractor comprised of an inlet channel, two Coanda steps, a diverging chamber, two asymmetric feedback channels, a splitter, and an outlet channel was designed using the Coanda effect. The microextractor can passively mix two immiscible liquids to complete an extraction process. Using visualization and mass transfer experiments, the microextractor with asymmetric feedback channels was experimentally investigated at high Reynolds numbers (Re > 120), and the results for this device were compared with results obtained from symmetric feedback channels. This investigation reveals that non-recirculating flows, recirculating flows through feedback channels, two vortex flows on both sides of the splitter, and oscillation become more prominent with increasing Reynolds numbers. Compared with symmetric feedback channels, asymmetric feedback channels provide more unbalanced transverse forces. In contrast with the symmetric microextractor, the asymmetric microextractor disperses the aqueous phase effectively and creates more intense oscillation. Using a 3-mol/L HNO3 solution and a 30% tributyl phosphate-kerosene solution as the aqueous phase and the organic phase, respectively, the mass transfer experiments also prove that asymmetric feedback channels improve the microextractor's efficiency, and 97.1% extraction efficiency (acid distribution coefficient/equilibrium acid distribution coefficient) was achieved. (C) 2014 Elsevier B.V. All rights reserved.