IPCC third report says that we have still a lot of uncertainties to predict global warming even using latest GCMs. Regarding atmospheric radiation, uncertainty of the radiative forcing is still large, which is mainly caused by aerosols, clouds, and water vapor interacting among them. National Space Development Agency of JAPAN (NASDA) and Communications Research Laboratory (CRL) started Phase-A study with European Space Agency (ESA) in the EarthCARE project. The objectives of EarthCARE project are to observe vertical and horizontal distributions and physical characteristics of aerosols and clouds from a satellite, and also to measure the precise Earth radiation budget simultaneously. Finally we will be able to evaluate physical processes of clouds and aerosols regarding the radiative budget and forcing. The EarthCARE satellite carries 5 sensors, namely Cloud Profiling RADAR (CPR), Atmospheric LIDAR (ATLID), Multi-Spectral Imager (MSI), Broad Band Radiometer (BBR) and Fourier Transform Spectrometer (FTS). The result of the pre-Phase A study shows the synergy observation benefits using some compensative combinations of sensors, such as CPR/ATLID for clouds, ATLID/MSI for aerosols, BBR/FTS for the radiation budget. NASDA and CRL are studying FTS and CPR, respectively. CPR is a 94GHz RADAR using 2.5m diameter reflector with Doppler measurement mode. The sensitivity is -38dBZ. The vertical and horizontal resolution is 100 m, 1 km, respectively. FTS is a Michelson interferometer of which spectral measurement range is from 5.7 μm to 25 μm with 0.5 cm-1 unapodized spectral resolution. FOV is 10 km by 10 km. EarthCARE is planned to be launched in 2008 for 2 years mission. Phase-A study will continue until the end of 2003.