Ionizing radiation produces excessive reactive oxygen species (ROS) which impose detrimental effects on biological systems. Thus, it is important to explore clinically safe and efficacious radioprotection agents to scavenge ROS and reduce the risks of radiotherapy. Recently, emerging catalytic nanomaterials such as sulfide nanomaterials have shown capability of clearing ROS in vivo by unique electron transfers between atoms, but their catalytic activities are yet suboptimal. As such, there is an unmet need to improve catalytic properties for stronger antioxidant activities and radiation protection. Herein, we prepared ultrasmall Au-MoS clusters (∼2.5 nm) and they showed enhanced catalytic properties via gold intercalation facilitating increased active sites and synergistic effects. Electrocatalysis results revealed that the catalytic activity of Au-MoS towards HO was superior to ultrasmall MoS without Au. As a result, we found that improving the electrocatalytic property of Au-MoS can effectively enhance corresponding antioxidant activities and radioprotection effects in vivo. In addition, Au-MoS also showed significant radioprotection in vitro and dramatically reduced the excess of radiation-induced adverse ROS. It also rescued radiation-induced DNA damages and protected the bone marrow hematopoietic system from ionizing radiation.