The corrected multiyear ice (MYI) concentration product from the University of Bremen, Institute of Environmental Physics (IUP), is being retrieved with a two-step algorithm:(1) A constrained optimisation technique that uses different sets of microwave satellite data and the probability distributions of radiometric signatures of different ice types whose concentration (area fraction) is to be retrieved. This is the Environment Canada Ice Concentration Extractor (ECICE) [Shokr et al. 2008, Shokr and Agnew 2013]. The input data used here are microwave radiometer data at 18 and 37 GHz (horizontal and vertical polarisation) from the instrument AMSR2 (Advanced Microwave Scanning Radiometer 2) on the JAXA satellite GCOM-W1, as well as microwave scatterometer data from ASCAT on the European satellites MetOp-A and -B.(2) Two correction schemes for the output from ECICE in order to correct for anomalous radiometric and backscatter observations. Such anomalies are caused by snow wetness and metamorphism. This happens when air temperature rises and approaches the melting point. Air temperature from meteorological reanalysis data used in one correction scheme and sea ice drift is used in the second [Ye et al. 2016a, 2016b]. The data are gridded on a polar stereographic grid (EPSG code 3412, Antarctic) with 12.5 km grid resolution. Further details are explained in the MYI User Guide (https://seaice.uni-bremen.de/data/MultiYearIce/MYIuserguide.pdf).Caveats: This is the first data set of Antarctic multiyear sea ice. Rough young ice and first year ice might erroneously be detected as MYI, and in the vicinity of grounded icebergs, spurious MYI can occur that further spreads during the freezing season.