For two VIKING orbits crossing the night oval source region of Auroral Kilometric Radiation (AKR), we derive the AKR polarization from the cutoff-frequencies and from the spin modulated pattern of the emission. The R-X mode is predominant, but can be accompanied by L-O mode and Z mode band. The Z mode is observed continuously from inside the plasmasphere to the AKR source region. An offset in the spin modulation pattem near the AKR source region during one of the orbits shows that steep gradients of the plasma density at the edge of the source region can play an important role for the orientation of the wave polarization plane or for the mode conversion. ¿American Geophysical Union 1987