The solar Occultation RAdiometer (ORA) is a seven broadband channel instrument working in the UV to near-IR range, that was launched in 1992 on board the EUropean REtrievable CArrier for a 1-year mission. About 7000 orbital occultations of the Sun have been recorded and processed through vertical and spectral inversions. Starting from the wavelength dependence of the retrieved aerosol extinction coefficient, properties of particle size distribution have been derived within the frame of the Mie theory, with a vertical regularization. The inversion algorithm will be presented as well as important results about the time evolution of stratospheric aerosols in the post-Pinatubo period. Global profiles of particle size distribution properties will be presented and interpreted.