Polarization measurements of the twilight background with Wide-Angle Polarization Camera (WAPC) are used to detect the depolarization effect caused by stratospheric aerosol near 20 km altitude. Based on a number of observations in central Russia in spring and summer 2016, we found the parameters of lognormal size distribution of aerosol particles. This confirmed the previously published results of the colorimetric method as applied to the same twilights. The mean particle radius (about 0.1 mu m) and size distribution are also in agreement with the recent data of in situ and space-based remote sensing of stratospheric aerosol. The methods considered here provide two independent techniques of the stratospheric aerosol study based on the twilight sky analysis.