A passive micromixer based on the concept of a three-dimensional serpentine split-and-recombine (SAR) microchannel using a series of "OH"-shaped segments was developed, and the flow and mixing performances were numerically analyzed using Navier-Stokes and mass conservation equations with a diffusion-convection model in a Reynolds number (Re) range of 0.1 <= Re <= 120. The two working fluids were water and ethanol. A mixing index based on the variance of the mass fraction of the mixture was employed to evaluate the mixing performance of the micromixer. To analyze the effects of geometry on the mixing performance a parametric study was conducted using three geometric parameters and the Reynolds number. The introduction of the SAR concept in the design of the serpentine micromixer was found to improve the mixing performance over the tested Reynolds number range, and the proposed micromixer achieved a mixing index of 0.884 at Re =30. (C) 2015 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.