In this paper AIRS cloud mask is objectively determined from the accurately co-located MODIS 1 km cloud mask information within each of the AIRS field of view. The AIRS cloud mask is becoming one of the most critical initial information for any of the AIRS data utilities such as, clear radiance data assimilation, sounding retrieval, cloud property study, land and sea surface temperature retrieval, aerosol/dust detection, and spectroscopy analysis, just to name a few.