Abstract Because of the ability to induce cell death in certain conditions, the fullerenes (C60 ) are potential anticancer and toxic agents. The colloidal suspension of crystalline C60 (nano-C60 , n C60 ) is extremely toxic, but the mechanisms of its cytotoxicity are not completely understood. By combining experimental analysis and mathematical modelling, we investigate the requirements for the reactive oxygen species (ROS)-mediated cytotoxicity of different n C60 suspensions, prepared by solvent exchange method in tetrahydrofuran (THF/ n C60 ) and ethanol (EtOH/ n C60 ), or by extended mixing in water (aqu/ n C60 ). With regard to their capacity to generate ROS and cause mitochondrial depolarization followed by necrotic cell death, the n C60 suspensions are ranked in the following order: THF/ n C60 >EtOH/ n C60 >aqu/ n C60 . Mathematical modelling of singlet oxygen (1 O2 ) generation indicates that the1 O2 -quenching power (THF/ n C60 <EtOH/ n C60 <aqu/ n C60 ) of the solvent intercalated in the fullerene crystals determines their ability to produce ROS and cause cell damage. These data could have important implications for toxicology and biomedical application of colloidal fullerenes.