Abstract: Deep-sea microorganisms play an important role in organic matter mineralization. The ultimate fate and microbial impact of recalcitrant dissolved organic carbon (RDOC) in the deep sea still need to be further researched. In this study, microbes of water samples at different depths (200-4 700 m) of 6 stations in the western Pacific Ocean were enriched with humic acid and landfill leachate at low temperature for one year, respectively. Bacterial diversity was analyzed using 16S rRNA gene high-throughput sequencing technology. Results showed that the bacterial compositions of enriched samples with different substrates were similar. The dominant genera contained Alcanivorax, Methylophaga and Polycyclovorans of Gammaproteobacteria, Thalassospira and Paracoccus of Alphaproteobacteria and Nocardioides of Actinobacteria. The dominant bacteria may participate in the deep mineralization of RDOC in situ.