In this study, newly devised is a magneto-hydrodynamic (MHD) micro-mixer capable of differential pumping of two different miscible fluids, and numerically investigated are the mixing performance and the mass flow rates of the two fluids. By artfully applying different potentials to different electrode pairs, Lorentz-force with different sizes can be created, driving the liquids in a desired direction for pumping, and inducing fluid circulation at a cross-section for mixing. The results show that the micro-mixer proposed in this study can achieve high mixing performance for electrolytes, together with differential pumping capabilities for the two different miscible fluids. The effect of the total difference in potential applied to the electrodes in pumping section on the mixing performance is numerically analyzed. Also, rectangular and H-shaped cross-sections for pumping section have been examined to explore the geometrical effect on the differential pumping capability. (C) 2018 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.