Backscattered radiation measurements from the shuttle solar backscatter ultraviolet spectral radiometer were used to examine aerosol optical properties and a possible ozone decrease in the tropical region after the eruption of Mt. Pinatubo. Observations made on two flights separated in time by 10 months show that backscattered ultraviolet radiation was greatly enhanced after the eruption as compared to the earlier measurements. The enhancements in backscattered radiation exhibit a special wavelength dependent signature. The peak percentage enhancement was found near 302 nm for solar zenith angles greater than 20¿, corresponding to the latitude band 14¿S--14¿N. Radiative transfer calculations indicate that the wavelength dependence of the enhancement is consistent with an ozone decrease in the altitude region of the Pinatubo aerosol clouds. The Pinatubo aerosol optical depth was found to vary in the range 0.07--0.53 in the ultraviolet region at tropical latitudes. Furthermore, a 16--22 Dobson unit decrease of ozone in the altitude region occupied by the aerosol cloud is consistent with the spectral dependence of the enhanced backscattered radiance. ¿ American Geophysical Union 1995