The impacts of ATOVS and SSM/I data in MERRA are investigated with observing system experiments (OSE). For the observation from each platform, we have performed a two year OSE. That is a two year reanalysis segment parallel the original MERRA stream but withholding the targeted observation type from assimilation. By comparing the original MERRA data with these observation withholding reanalysis segments, we obtained systematic pictures of the impacts from ATOVS and SSM/I. Detailed structure of the impacts from each platform will be shown. Then the similarity and difference between the impacts, the mechanisms of these impacts and the associated implication in reanalysis application will be discussed.