Significance: Although many microbial explorations for hadal sediments began in the 1950s, the hadal water is the least-explored microbial biosphere. In this study, unexpected microbial ecosystems associated with the hadal trench water were discovered down to a 10,257-m water depth in the Challenger Deep of the Mariana Trench, which is the deepest ocean on Earth. We found the enrichment of heterotrophic population in the hadal water (6,000 ∼10,257 m) microbial communities, whereas the chemolithotrophic populations were more abundant in the upper abyssal waters. This observation suggested that the hadal microbial biosphere was supported by the endogenous recycling of organic matter in the hadal waters associated with the trench geomorphology.