There is a general view that the auroral kilometric radiation (AKR) polarization is fully circular with dominating right-hand extraordinary mode and some admixture of the left-hand ordinary mode. Most of up-to-date determinations of the wave modes of the AKR have been based on measurements of the circular component of the wave polarization, leaving the linear polarization parameters unknown. In space observations the polarimeter is usually not directed to the AKR source. However, having determined the polarization parameters in each of the three perpendicular planes, one is able to determine the polarization ellipse in the 3-D space. Results of statistical estimations of the AKR polarization parameters in the wave plane are presented. Data were provided by the Interball-2/Polrad triaxial polarimeter. It is the first time the dynamic spectra of all four Stokes parameters of the AKR are displayed in the wave plane. The AKR polarization is mostly circular with an estimated mean value of the semiaxes ratio of 0.99 ± 0.10 rms error, with a small contribution of the linear component at a level of 0.07 ± 0.09 rms error, and an unpolarized component at a level of 0.10 ± 0.08. The uncertainties of these estimations are too large to definitely conclude on presence or absence of some small contributions of the linear and upolarized components in the AKR. However, in the limits of the above uncertainties these estimations do not contradict expectations that the linear polarization is absent in the AKR. Some small contribution of the unpolarized component can be explained by a relatively high level of noise and board interefences.