In this paper, a magnetohydrodynamic (MHD) microfluidic switch, which could form the basis for general microfluidic circuits, is reported. The switch uses an AC MHD pumping mechanism in which the Lorentz force is used to pump electrolytic solutions. By integrating two AC MHD pumps into different arms of a Y-shaped fluidic circuit, flow can be switched between the two arms by activating one of the micropumps and setting the other one at a counteracting pressure to prevent flow. Flow could be switched from one microchannel to another at a velocity of 0.3 mm/sec. This type of switch is easily integrated with other biochips and can be used to produce complex fluidic routing, which may have multiple applications in micro total analysis systems (TAS). Examples of applications include on-chip combinatorial chemistry for drug discovery and drug testing, connectors for routing samples to different detectors, and general reconfigurable assays.