Abstract: We report the design and fabrication of microfluidic chips based on the electrorheological (ER) fluid mechanism. An ER fluid has a viscosity that increases as the applied field strength increases, is reversible, and has a fast response time on the order of 1—10 ms, making it an ideal material for microfluidic valves with digitally-control characteristics. With such a valve we have successfully fabricated a series of microfluidic devices, such as a microfluidic mixer, micro-damper and micro-pump.