A flow-analysis method using Navier-Stokes equations has been applied to a parametric study on a micromixer with a modified Tesla structure, and an optimization of this micromixer has been performed with a weighted-average surrogate model based on the PRESS-based-averaging method. The numerical solutions are validated with the available numerical and experimental results. The mixing performance and pressure-drop have been analyzed with two dimensionless parameters, i.e., the ratio of the diffuser gap to the channel width, theta, and the ratio of the curved gap to the channel width, phi, for a range of Reynolds numbers from 0.05 to 40. The shape of the microchannel is optimized at the Reynolds number of 40 with two objectives: the mixing index at the exit and the friction factor. The "naive approach" has been applied to realize a single-objective optimization problem. The optimization results reveal that the mixing and pressure-drop characteristics are very sensitive to the geometric parameters. Sensitivity analysis reveals that in the vicinity of the optimum point, the objective function is more sensitive to phi as compared to theta. (C) 2010 Elsevier B.V. All rights reserved.