We show that bimetallic nanoparticles (NPs) of AuPt without any surface modification are potent antibiotic reagents, while pure Au NPs or pure Pt NPs display no antibiotic activities. The most potent antibacterial AuPt NPs happen to be the most effective catalysts for chemical transformations. The mechanism of antibiotic action includes the dissipation of membrane potential and the elevation of adenosine triphosphate (ATP) levels. These bimetallic NPs are unique in that they do not produce reactive oxygen species as most antibiotics do. Being non‐toxic to human cells, these bimetallic noble NPs might open an entry to a new class of antibiotics. No side‐effect: Bimetallic nanoparticles of AuPt are potent antibiotic reagents with low cytotoxicity. The antibiotic mechanism includes the rupture in the bacterial inner membrane and the increase of intracellular adenosine triphosphate levels, but does not involve the generation of reactive oxygen species (see picture).