The industrial production of active proteins from E. coli necessitates the refolding of high concentrations of protein over a short period of time. However, it is difficult to simultaneously achieve high concentration and short residence time. The dialysis method can refold high concentrations of proteins, but this process takes a long time. The dilution method can quickly refold proteins, but the resultant proteins are inevitably diluted. In the present study, by designing microchannels in dialysis membranes, which can enlarge the surface area for quickly removing protein denaturant, high concentrations of active carbonic anhydrase---eight times more concentrated than achieved using dilution method---were refolded in 20 minutes, which is orders of magnitude faster than the conventional dialysis method.