Relative extinction coefficients as a function of wavelength are determined for stratospheric aerosols from the Mount Pinatubo eruptions in June of 1991, using the Halogen Occultation Experiment (HALOE) data at latitudes 20¿--55¿ in the northern hemisphere from November 1991 to February 1992. Extinction coefficients at each of the eight HALOE channels are obtained from the ratio of two transmittance profiles of consecutive occultation measurements separated by 25¿ longitude, one loaded with aerosols larger than the other during the early stage of aerosol dispersion after the eruptions. These coefficients are compared to theoretical Mie calculation values. Composition and a single mode particle size distribution are derived as a function of altitude. The retrievals indicate that the weight percentage of H2SO4 for 45 occultation cases is larger than the equilibrium value by about 5 wt %, while the size distribution parameters are within the range of those measured in situ at Laramie, Wyoming. ¿ 2001 American Geophysical Union