A flow analysis method using Navier-Stokes equations has been applied to a parametric investigation of mixing two fluids in a three-dimensional serpentine microchannel, which has not been reported so far. The serpentine microchannel with "L-shaped" repeating units is found to be effective in mixing fluids at Reynolds numbers, 1, 10, 35 and 70. Mixing performance and pressure drop characteristics with two geometrical parameters. i.e., the ratio of channel height to channel width and the ratio of the length of a straight channel in an "L-shaped" unit to the channel width, have been analyzed at four different Reynolds numbers. A mixing index has been used to quantify and elucidate mixing behavior in the microchannel. The vortical structure of the flow in the channel is also analyzed to identify the relationship with mixing performance. The results reveal that mixing and pressure drop characteristics in a serpentine channel are very sensitive to the geometric parameters, showing different behavior at various Reynolds numbers. (C) 2008 Elsevier B.V. All rights reserved.