Photoactive semiconductors as bactericidal tools play an important role in various industries. These materials rely on the external stimulus of photoirradiation to generate reactive oxygen species (ROS), which limits their practical application to more general environments. Herein, a simple Zn/ZnO core/shell structure which continuously generates ROS without external energy input (in the dark) is developed. The core/shell structured Zn/ZnO particles showed excellent antibacterial activity when tested as surface coating, killing Gram-negative bacteria, Gram-positive bacteria and fungus, with more than 8-log cell reduction. Due to the spontaneously generated ROS, the Zn/ZnO core/shell particles can degrade dyes in the absence of light. Further study showed that the Zn/ZnO particles generate a high concentration of ˙O2− and H2O2 radicals which killed the bacteria and degraded the dyes. The generation of ROS without an external stimulus was proposed to be due to zinc corrosion and electron transfer processes. This new material provides a potential solution for general disinfection and environmental sanitation.