The most stable structures of polyhydroxylated metallofullerene Gd@C-82(OH)(x) (x = 1-24) were investigated using density functional theory calculations. After examining a number of structural isomers, some rules about the locations of hydroxyl groups on the endohedral fullerene cage of Gd@C-82 were proposed. The hydroxylated carbon atoms tend to enclose two opposite six-membered rings for the most stable Gd@C-82(OH)(12) and seven six-membered rings for the most stable Gd@C-82(OH)(24), respectively. The hydroxyl groups prefer to locate on para-position of the six-membered ring or meta-position of the five-membered ring. (C) 2010 Elsevier B.V. All rights reserved.