Mixing performance of four types of mixers was investigated for Newtonian and shear-thinning fluids using numerical simulation. The four mixers considered were with the following blade designs: rectangular blade, one Z-blade, two Z-blades, and three rotating pins. Finite element method was used to compute velocity profiles, pressure and stress distributions in the mixing chamber. Mixing effectiveness was evaluated by the flow number and volumetric strain rate. It was demonstrated that shear flow was dominant in rectangular, one Z-blade, and two Z-blade mixers; in the mixer with three rotating pins elongational flow was significant making it the most effective for dispersive mixing. The largest volumetric strain rate was predicted in the mixer with two Z-blades. The rectangular blade mixer was deemed due to a large stagnant region observed. The stagnant regions were larger near the wall for all mixers when shear-thinning fluid was used compared to the Newtonian fluid. Thus, for shear-thinning fluids, to achieve the same mixing effect as with Newtonian fluid, either a smaller gap between the blade and the wall or a higher blade speed is required. Overall, the two Z-blade mixer was considered the best in terms of mixing effectiveness. (c) 2005 Published by Elsevier Ltd.