Publications concerning the mechanism of biological activity, especially the immunological mechanism of C(60)(OH)(20) nanoparticles, are relatively limited. However, the structure and characteristics of this carbon allotrope have been widely investigated. In this paper, we have demonstrated that water-soluble C(60)(OH)(20) nanoparticles have an efficient anti-tumor activity in vivo, and show specific immunomodulatory effects to the immune cells, such as T cells and macrophages, both in vivo and in vitro. For example, C(60)(OH)(20) nanoparticles can increase the production of T-helper cell type 1 (Th1) cytokines (IL-2, IFN- gamma and TNF-alpha), and decrease the production of Th2 cytokines (IL-4, IL-5 and IL-6) in serum samples. On the other hand, C(60)(OH)(20) nanoparticles show almost no adverse effect to the viability of immune cells in vitro but stimulate the immune cells to release more cytokines, in particular TNF- alpha, which plays a key role in the cellular immune process to help eliminate abnormal cells. TNF- alpha production increased almost three-fold in treated T lymphocytes and macrophages. Accordingly, we conclude that C(60)(OH)(20) nanoparticles have an efficient anti-tumor activity and this effect is associated with an increased CD(4)(+)/CD(8)(+) lymphocyte ratio and the enhancement of TNF- alpha production. The data suggest that C(60)(OH)(20) nanoparticles can improve the immune response to help to scavenge and kill tumor cells.