Presented at the 2013 Aquarius/SAC-D Science Team MeetingThis paper presents an assessment of the MWR brightness temperature calibration. The MWR TBs can be used to produce reliable co-located water vapor, cloud liquid water and precipitation estimates that can be used to flag or even supplement the Aquarius salinity retrieval. Additionaly, MWR TBs may improve the Aquarius roughness correction. To this end, it is important to ensure that the TBs are stable and well inter-calibrated between the beams that are used to form the swath. We employ several methods to assess the TB calibration. To assess the overall calibration, the MWR TBs are compared to hot and cold on-Earth brightness temperature references originally developed for the Jason series altimeter radiometers operating at similar frequencies. In addition to these previously developed methods, a new method is employed to specifically assess the inter-beam TB calibration over the full dynamic range. The method finds homogeneous areas over the ocean and land where observations across the region are uncorrelated with observing location, meaning the long term average will reduce to a common mean for each MWR beam at common incidence angle. Results will be presented showing the quality of the version 6 MWR TB inter-beam calibration, absolute calibration relative to the on-Earth references and stability over time.