The industrial implementation of enzymes in flow biocatalysis microreactors is expected to be essential for the emergence of a bio-based circular economy. Major challenges concern the efficient immobilization of delicate enzymes inside miniaturized reactors without compromising their catalytic activity. We describe the exploitation of the widely used His-tag system in a microfluidic packed-bed reactor that contains ketoreductase-functionalized magnetic beads. In a continuous process, these reactors produced highly stereoselective (R)-configured alcohols (d.r. 99:1) with an average conversion of > 90 % for more than 4 days. We believe that such miniaturized flow reactors can be of great utility for future sustainable production processes.