Hydrophilic endohedral <SUP>133</SUP>Xe-fullerenols [<SUP>133</SUP>Xe@C<SUB>76</SUB> (OH) <SUB>x</SUB> and <SUP>133</SUP>Xe@C84 (OH) <SUB>x</SUB>] were synthesized from hydrophobic endohedral <SUP>133</SUP>Xe-fullerenes. The yields were found to depend on the solubility of endohedral <SUP>133</SUP>Xe-fullerenols in ο-dichlorobenzene and water phases, reflecting the number of OH groups of the product. The endohedral <SUP>133</SUP>Xe-fullerenols stored in 0.9% NaCl solution at 20°C were stable enough for the use in nuclear medicine.