Large increases of stratospheric aerosol particles caused by the eruption of Mexican volcano El Chichon in early April 1982 were observed by a Yag lidar system at two wavelengths (1.06 &mgr;m and 0.53 &mgr;m) over Fukuoka for three months since April 18. Most of the observations show high concentrations of aerosols in the altitude regions from 15 to 33 km, with highest concentrations between 21 and 30 km. The aerosol optical thickness at 0.55 &mgr;m is about 0.1-0.3; this is about 10 to 30 times the maximum monthly mean values that were observed after the Mt. St. Helens event in 1980. The mean radius of aerosols in the densest part of the El Chichon cloud is estimated to be approximately 0.1 &mgr;m. This estimate is based on the slow settling velocity of the peak of the cloud and from information obtained by comparison of the two-wavelength lidar returns. A significant impact of the presence of the cloud on the climate through variations of atmospheric circulation is suggested.