[Gd@C82(OH)22]n particles (22 nm in a saline solution) of a dose level as low as 10(-7) mol/kg exhibit a very high antineoplastic efficiency ( approximately 60%) in mice. A dose increment of 1 x 10(-7) mol/kg increases the tumor inhibition rate 26%. [Gd@C82(OH)22]n particles have a strong capacity to improve immunity and interfere with tumor invasion in normal muscle cells, nearly without toxicity in vivo and in vitro. Unlike conventional antineoplastic chemicals, the high antitumor efficiency of nanoparticles is not due to toxic effects to cells because they do not kill the tumor cells directly and only about 0.05% of the used dose is found in the tumor tissues. Results suggest that fullerene derivatives with proper surface modifications and sizes may help realize the dream of tumor chemotherapeutics of high-efficacy and low-toxicity.