ASTER is a high resolution optical sensor for observing the Earth in a five-year mission on the EOS AM1 platform to be launched in 1998. ASTER consists of three radiometers. VNIR has three bands in the visible and near-infrared region, SWIR has six bands in the shortwave infrared region, and TIR has five bands in the thermal infrared region. The ASTER project is establishing a calibration plan including calibration requirements to the contractors. The major instrument characteristics specified are spectral characteristics, offset, nonlinearity of response, absolute responsivity, polarization effect and stray light effect. The ASTER pre- flight calibration of VNIR and SWIR adopts the working standard large integrating sphere of 1 m in diameter whose radiance levels are traceable to the primary standard fixed point blackbody. This is similar to the prelaunch calibration system of OPS of JERS-1 launched in 1992. The onboard calibration devices of VNIR and SWIR are halogen lamps and photodiode monitors used once in sixteen days. These calibrators are duplicated and used alternately to increase the reliability. The offsets of VNIR and SWIR are checked by looking at the dark side of the Earth. The TIR is unable to see the dark space. The temperature of the onboard blackbody of TIR remains at 270 K in the short term calibration for the offset calibration, and is varied from 270 K to 340 K in the long term calibration for the offset and gain calibration once in sixteen days. The TIR onboard blackbody is calibrated against a standard blackbody in a vacuum chamber before launch. The standard blackbody has a hood of 330 mm diameter and 600 mm length, the emissivity of more than 0.995 and the temperature range of 100 K to 400 K.