The 3-D hydrodynamics of shear thinning fluids in a stirred tank with an anchor impeller were numerically simulated. By using a computational fluid dynamics code (CFX 13.0), the obtained results give a good prediction of the hydrodynamics such as the velocity fields and cav size. The multiple reference frames (MRF) technique was employed to model the rotation of the impellers. The rheology of the fluid was approximated using the Ostwald model. To validate the CFD model, some predicted results were compared with the experimental data and a satisfactory agreement was found. The effects of impeller speed, fluid rheology, and some design parameters on the flow patt, cav size and power consumption were explored.