Biocatalysts In article number 2200255, Yi Wang, Li Qiu, Chong Cheng, and co-workers report a library of reactive oxygen species (ROS)-catalytic metalloenzyme-mimics with different types of atomic metal centers; the catalytic activities, substrate selectivities, and ROS products are compared. These biocatalysts show high ROS-catalytic performances and it is found that the catalytic activities are highly related to the electronic structures of the metal centers.