The chemical generation of singlet oxygen (1O2) by the MoO42−‐catalyzed disproportionation of hydrogen peroxide (H2O2) has been widely applied in numerous catalytic processes; however, such molybdate ions cannot be administered for redox‐based cancer therapeutics. This work reports the albumin‐mediated biomimetic synthesis of highly active molybdenum sulfide (denoted MoB) nanocatalysts that mediate the simultaneous generation of 1O2 and superoxide anion (O2•−) from H2O2, which is relatively abundant in malignant tumors. The MoB‐catalyzed reactive oxygen species (ROS) are able to activate the ferroptosis pathway and cause lipid peroxidation for efficient cancer therapy. Furthermore, for the first time, the catalytic activity of MoB is visualized in situ. Moreover, a catalytic imaging modality based on MoB is developed for specific imaging of inflammation diseases without background interference. Therefore, this study presents a biomimetic strategy toward Mo‐based nanocatalysts for ROS‐facilitated tumor ferroptosis and catalytic imaging.