Viral abundance in deep-sea environments is high. However, the biological, ecological andbiogeochemical roles of viruses in the deep sea are under debate. In the present study,microcosm incubations of deep-sea bacterioplankton (2,000 m deep) with normal andreduced pressure of viral lysis were conducted in the western Pacific Ocean. We observed anegative effect of viruses on prokaryotic abundance, indicating the top-down control ofbacterioplankton by virioplankton in the deep-sea. The decreased bacterial diversity and a different bacterial community structure with diluted viruses indicate that viruses are sus-taining a diverse microbial community in deep-sea environments. Network analysis showedthat relieving viral pressure decreased the complexity and clustering coefficients butincreased the proportion of positive correlations for the potentially active bacterial com-munity, which suggests that viruses impact deep-sea bacterioplankton interactions. Ourstudy provides experimental evidences of the crucial role of viruses in microbial ecology and biogeochemistry in deep-sea ecosystems.