This work describes retrieval algorithms for stratospheric aerosols based on the wavelength dependency of their extinction measurements to be obtained by ADEOS/ILAS in 1990. To estimate the chemical composition and size distribution, the aerosols are assumed to be sulfuric acid-water droplets, and the lognormal representation is employed for their size distribution. It is shown from model calculations with an ILAS simulator that 75%H2SO4 is a main component of stratospheric aerosols, and size of aerosols gradually decreases with altitude.