The rapid advancement of photodynamic therapy (PDT) antibacterial materials has led to promising alternatives to antibiotics for treating bacterial infections. However, antibacterial drugs have poor light absorption and utilization rates, which limits their practical application. Constructing two-dimensional (2D) heterojunctions from materials with matching photophysical properties has emerged as a highly effective strategy for achieving high-efficiency photo-antibacterial performance. Here, we designed and prepared an atom co-sharing Bi/ Bi 4 O 5 Br 2 nanosheet heterojunction by a simple in situ reduction. This heterojunction material combines outstanding biocompatibility with excellent bactericidal efficiency, which exceeded 90 % against Escherichia coli (a Gram -negative bacterium) and Staphylococcus aureus (a Gram-positive bacterium) under visible light irradiation, around nine-fold higher than that with pure Bi 4 O 5 Br 2 nanosheets. The results suggest that localized surface plasmon resonance (LSPR) of shared Bi atoms on the Bi 4 O 5 Br 2 nanosheets promotes light utilization and the separation and transfer of photo-generated charges, thus producing more abundant reactive oxygen species (ROS), which can partake in the PDT antibacterial effect. Our study underscores the potential utility of LSPRenhanced Bi-based nanosheet heterojunctions for safe and efficient PDT to combat bacterial infections.