Stable fullerene water suspensions (nC60) exhibited potent antibacterial activity to physiologically different bacteria in low-salts media over a wide range of exposure conditions. Antibacterial activity was observed in the presence or absence of light or oxygen, and increased with both exposure time and dose. The activity was also influenced by the nC60 storage conditions and by the age of the buckminsterfullerene (C60) used to make nC60. These results reflect the potential impact of nC60 on the health of aquatic ecosystems and suggest novel alternatives for disinfection and microbial control.