This paper presents the effect of positive dihedral (lean) on the aerodynamic performance of a low speed axial fan. The blade profiles of the reference (base) fan are stacked on a radial line at the centre of gravity of each profile. The stacking line of the fan with the dihedral, along which the blade profiles are shifted in the direction perpendicular to the chordline, makes an angle of 45 degrees in the radial direction. The performances of the both fans are investigated by means of ANSYS CFX commercial CFD software and are validated by experiments. Both of the computational and the experimental results show that positive dihedral removes the unstable operation region of the fan. Moreover, the total pressure rise and the total-to-total efficiency are increased at low flowrates. The detailed investigation shows that the induced radial velocity in the outward direction may be the reason of the positive effect of the dihedral at low flowrates. As a result, dihedral stacking extends the stable working range of the fan by removing the unstable region.