The knowledge of detailed 3D-flow field in a rotor axial-flow fan is crucial both for the correct evaluation of aerodynamic efficiency and for the improvement of the design of this turbomachine. These goals may be reached either by using a reliable fluid dynamic computational code or by performing detailed experimental investigations. In this paper a comparison is presented between experimental data and numerical results downstream of an industrial axial flow fan at two different load conditions. In spite of the complex three-dimensional flow, the strong secondary effects and the wide boundary layers experimentally observed downstream of the rotor, numerical results show a remarkably good agreement with measurements. These results show that the use of CFD in the design process may give a strong impulse to the development of more performing fans in the near future.