We present the successful design and fabrication of push-and-pull microvalves that use a giant electrorheological (GER) fluid. Our multilayer microvalves, including the GER fluid control channel, the electrode, the flow channel, and the flexible membrane, are fabricated with polydimethylsioxane-based materials by soft lithography techniques. The GER effect is able to provide high-pressure changes in GER control channel so as to fully close and open an associated flow channel. The fast response time of the GER fluid and the push-and-pull valve design adopted assure fast switching time of the valve less than 10ms and sound reliability. This GER-fluid-based microvalve has other advantages of easy fabrication and biocompatibility and is suitable for most microfluidic applications.