This article assesses the impact of Advanced Microwave Scanning Radiometer 2 (AMSR2) radiances in the all-sky assimilation of the European Centre for Medium-Range Weather Forecasts (ECMWF). Individual impacts of three microwave imagers including AMSR2 were examined by using a baseline experiment that had no microwave imager data. The three microwave imagers brought similar improvements in humidity, temperature and wind first-guess (FG) fields in the troposphere. Improvements were found in fits to both analyses and other observations. Moreover, significant improvements in wind and geopotential height fields in the troposphere were found in day 3–6 forecasts. AMSR2 made larger improvements than other microwave imagers to geopotential height forecasts in the Northern Hemisphere. The use of AMSR2 radiance data in addition to the other existing microwave imagers gave mixed results. Consistent improvements in the FG fit to humidity observations were confirmed. However, the FG fit for several channels of the microwave temperature sounding instruments was degraded. The mean FG departure of AMSR2 showed biases that varied according to the time of day and meteorological conditions. The causes of the biases were identified as insufficient representation of the cloud liquid water path (LWP) in the forecast model under unstable conditions and insufficient amplitude of LWP diurnal variation in stratocumulus areas in the Tropics. The assimilation of too much biased data might start to bring negative effects for the analyses and forecasts, which for some parameters could outweigh the improvements in the assimilation. However, despite this, AMSR2 brought significant improvements of the geopotential height field in the Southern Hemisphere lower troposphere for day 5–7 forecasts.