The object of this work was to evaluate the capability of numerical simulation to predict different features of non-Newtonian fluid mixing process. A relatively simple impeller (six bladed vane rotor) was used for the mixing of carboxymethyl cellulose. A LDA method was used to measure the tangential velocity at two points inside the mixing vessel. Using visualization, a significant vortex above the impeller was observed. The shape of the free surface was determined by a geometrical reconstruction of the images of the illuminated section. Torque on the impeller shaft was measured to determine the characteristics of the fluid. Fluent program package was used for the simulation. The problem is challenging since the effects of nonNewtonian fluid, mixing process and free surface have to be included in the simulation. The comparison between the experimental and numerical results confirms the accuracy of the simulations.