Experimentally characterized is a novel microseparator/classifier, whose functional part is an arc microchannel with a width of 200 mu m, depth of 150 mu m, and radius of 20 mm. First, a unique separation principle due to shear-induced lift force is visually demonstrated with neutrally buoyant particles. The device performance is subsequently measured in terms of cut size, separation sharpness, and feed pressure for slightly denser acrylic particles. Compared with representative hydrocyclones, the present device is found to attain significantly smaller cut size at comparable feed pressure, and vice versa. It is finally shown that the device performance remains highest below a critical Stokes number because of no or negligible shear-induced interparticle collisions. It is concluded that the device is to operate with a high efficiency based on the proposed Stokes number. (C) 2008 American Institute of Chemical Engineers AIChE J, 55: 2434, 2009