A computational study has been performed to determine the rates of mixing in a curved square duct at low Reynolds numbers of interest to microfluidic applications. Two flow streams with inlet scalar concentrations of zero and unity in the two halves of a duct perpendicular to the plane of curvature were allowed to mix by convection and diffusion. Concentration distributions and unmixedness coefficients are presented for several Reynolds and Schmidt numbers and are compared with values for a straight channel of equivalent length. It is seen that for large Schmidt number fluids, mixing is considerably enhanced at moderately low Reynolds numbers (Re similar to 10), but is not enhanced at Reynolds numbers of the order of 0.1. (C) 2004 American Institute of Chemical Engineers.