One of the series of satellite for the Global Change Observation Mission (GCOM) is the GCOM-W that will carry the Advanced Microwave Scanning Radiometer (AMSR) follow-on instrument. To keep the continuous observation by the current AMSR for the EOS (AMSR-E) on the Aqua satellite, an earliest launch date is desired. Current proposed launch year is 2010 in Japanese fiscal year. The AMSR-E instrument has been successfully operated for about 4-years and expected to continue providing measurements with high-spatial resolution and in C-band channels that are used to estimate all-weather sea surface temperature and land surface soil moisture. The total dataset period will be over 20-years if the AMSR-E observation can last until the GCOM-W launch. Among the GCOM mission objectives, GCOM-W will focus on the long-term observation of variations in water and energy circulation. In addition, further practical uses including numerical weather forecasting, maritime and meteorological monitoring, and ice applications will be promoted. The AMSR follow-on instrument will be a six-frequency, dual polarized passive microwave radiometer system to observe water-related geophysical parameters. It takes over the basic sensor concept of the AMSR-E instrument with some essential improvements on the calibration system and mitigation of radio-frequency interference (RFI) in C-band channels. Regarding the calibration system, some issues particularly for the warm load target will be investigated and improved based on the AMSR and AMSR-E experiences. Although mitigating the RFI problem is a difficult issue, some preliminary aircraft measurements of anthropogenic radio emissions have performed in Japan and used for assessing the possibilities of sub-band configuration in C-band. Prototyping the several critical components including the above has already started in the last Japanese fiscal year.