Optical properties of biomass burning aerosols in the event of Indonesian forest fires in 1997 were studied by groundbased sky radiometry and satellite remote sensing with AVHRR and TOMS radiometers. The AVHRR-derived optical thickness distribution agreed with the distribution of TOMS-derived UV-absorbing aerosol index and with the optical thickness measured by sky radiometry and sunphotometry. The single scattering albedo of aerosols was fairly constant as 0.9 in the September–October period. Relationship between Ångström turbidity factor and exponent supported the polydispersion consisted of aged small particles. This observation was consistent with the fact that the retrieved volume size distribution by sky radiometry has a distinct accumulation mode with a peak radius of 0.25 µm. Those optical properties of smoke aerosols seem to reflect the specific chemical structure of Indonesian forest fire aerosols, i.e., a mixture of carbonaceous and sulfate particles.