LANDSAT-5 TM images of the nuclear power plant of Chernobyl are analysed with the emphasis on estimating the reactor surface temperature. The investigation was done for TM channels 5 and 7 using the simulation model SENSAT developed at DFVLR. It accounts for the sensor characteristics (spectral response, IFOV) and target/background properties (size, temperature, emissivity). For the atmospheric part the LOWTRAN-6 model is used. The estimated surface temperature is 1000-1300 K for 29 April 1986, 3 days after the nuclear accident.