Hydrophilic nanoparticles of C-60 were prepared by cogrinding with 2-hydroxypropyl-beta-cyclodextrin (HP-beta-CyD) or gamma-CyD in a molar ratio 1:2 using an automatic magnetic agitating mortar for 3 It at 4 degrees C and reduced pressure. The nanoparticles (about 55 nm) in the gamma-CyD colloidal solution were significantly aggregated during storage at 25 degrees C, increasing in size to about 800 nm. On the other hand, the size of the C-60/HP-beta-CyD nanoparticles (about 90 nm) remained small for 28 days. C-60/HP-beta-CyD nanoparticles had a high propensity for generating superoxide anions. HP-beta-CyD is useful for preparation of hydrophilic nanoparticles of C-60 and preferred as an efficient stabilizing agent for pharmaceutical application of C-60.