Boron (B) doped bismuth oxybromide (B-BiOBr) nanosheets were synthesized using a hydrothermal method and their photocatalytic activities were investigated through inactivating a typical bacterium, Escherichia coli K-12 using fluorescence tubes as visible light (VL) sources. B atoms are successfully doped into the crystal lattice of BiOBr. However, the morphology, crystal structure, and {001}-facet exposed feature of B-BiOBr nanosheets remains unchanged compared with pure BiOBr nanosheets. Significantly, the as-prepared B-BiOBr nanosheets show superior activity in the photocatalytic inactivation of E. coli K-12 over pure BiOBr nanosheets under VL irradiation. Photogenerated h+ is evidenced to be the major reactive species accounting for the inactivation process of B-BiOBr. With its electron-deficient characteristics, the B dopant is favorable to accept extra e− from VB of BiOBr, leading to improved charge carrier separation efficiency. The greatly enhanced bacterial inactivation efficiency was attributed to the synergic advantages of enhanced VL adsorption capability and more amount of photogenerated h+ with higher oxidative ability. In addition, the destruction process of bacterial cell was also observed from the destruction of cell membrane to the intracellular components.