An inevitable consequence of the growth of applications and corresponding production of fullerenes is the accumulation of these molecules in natural aquatic environments and biological systems. This raises the issue of evaluating toxicity of fullerenes and its relation to physical characteristics of fullerene solutions under various conditions. The given paper presents a detailed structural characterization of associations of fullerenes C ₆₀ and C ₇₀ in aqueous suspensions prepared by various methods. The found different temperature and coagulation stability of the systems under study is related to different characteristic aggregate sizes after preparation. The potential correlation between physical and toxic properties of fullerene water solutions is discussed basing on the extended viability tests conducted for living cell cultures (mammalian fibroblasts of Chinese hamster).