Earth-abundant MoS2 with the advantages of a stable structure, tunable bandgap, and easy shear has great potential for applications in the fields of catalysis, biomedicine, and so on. However, the biocatalytic activity of MoS2 remains little investigated and is insufficient for biomedical applications. In this work, we develop ultra-small and water-soluble MoS2 clusters with superior antioxidant activity and enzyme-like activity via valence-engineering modulation with Ce doping. Compared with pure, Re-, Tl-, and Nd-MoS2 clusters, Ce-MoS2 clusters exhibit about 1.7-fold enhanced antioxidant activity. Moreover, superoxide dismutase (SOD)-like activity of Ce-MoS2 clusters is about 30-fold higher than that of MoS2 clusters. In addition, the Ce-MoS2 clusters are evidenced to possess ultra-high clearance performance for reactive oxygen species and reactive nitrogen radicals (RONS), especially ˙OH and O2˙-. The comprehensive analyses of valence evolution and the energy level structure indicate that the enhanced biocatalytic activity is attributed to the synergistic effect of valence engineering of Mo4+/Mo6+ and energy-level engineering in MoS2 clusters via Ce doping. This work provides a universal approach to improve the biocatalytic activity of MoS2 clusters via valence engineering modulation, which exhibits great potential in the field of biomedical application, especially inflammatory diseases.