SAGE II and SAGE III are two satellite experiments designed to measure aerosol extinctions and concentrations of trace gases in the atmosphere by using the techniques of solar and/or lunar occultation. SAGE II was launched in October 1984, while SAGE III was launched in December 2001. Four of the nine aerosol channels used by SAGE III are centered at wavelengths very close to that of the four SAGE II aerosol channels. Since 27 February 2002, the first day of SAGE III data set, there are occasions when SAGE II and III measurement locations on the same day are nearly coincident, thereby providing opportunities for a unique measurement comparison. In this paper, the comparison of aerosol extinctions and optical depths at four wavelengths measured by SAGE II and SAGE III in 2002 and 2003 is reported. It was found that in the main aerosol layer, between about 18 to 26 km, differences are less than about 30%. Larger differences are shown at altitudes near the tropopause and around 30 km. In general, SAGE III extinctions at 385 nm are higher than that measured by SAGE II, but the opposite is true for 1020 nm. At 452 nm, SAGE II and SAGE III extinctions are in good agreement and the differences are about 10 to 15%.