This study presents experimental results on the flow of magnetorheological grease (MRG) through microchannels. MR materials flowing through microchannels create microvalves. The flow is controlled by injecting the MRG through microchannels with controlled adjustable rates. To study the effect of different channel diameters and surface roughnesses, microchannels made of stainless steel, PEEK, and fused silica materials with nominal internal diameters ranging from 1 mm to 0.075 mm are tested. A magnetic field is applied perpendicular to the microchannel flow and is controlled by an input electric current. The pressure drop of the flow is measured across the length of the microchannels. The dynamic pressure drop range and surface roughness effects are also discussed. The Herschel–Bulkley model for non-Newtonian fluid flow is employed to the experimental results with good agreement. The results show a significant pressure drop for different magnetic field strengths.