As a part of fundamental studies for examining solubility controlling factors of metal complexes and applying supercritical extraction (SCE) method to the decontamination of solid radioactive wastes, solubility of Ln(fod)(3)center dot 2H(2)O (Ln = Pr, Nd, Eu, and Er, fod: 6,6,7,7,8,8,8-heptafluoro-2,2-dimethyl-3,5-octanedionate) and Ln(hfa)(3)center dot 2H(2)O complexes (Ln = Pr, Nd, Er, and hfa: 1,1,5,5,5-hexafluoro-2,4-pentanedionate) complexes in supercritical carbon dioxide (scCO(2)) was measured under conditions (Temp. = 40 degrees C, Pressure = 10-25 MPa) by using UV-vis spectrophotometer equipped with high-pressure cell. The solubility of Pr(fod)(3)center dot 2H(2)O, Nd(fod)(3)center dot 2H(2)O, Eu(fod)(3)center dot 2H(2)O, Er(fod)(3)center dot 2H(2)O, Pr(hfa)(3)center dot 2H(2)O, Nd(hfa)(3)center dot 2H(2)O, and Er(hfa)(3)center dot 2H(2)O complexes was evaluated as (1.32 +/- 0.03)x10(-1), (1.53 +/- 0.01)x10(-1), (1.59 +/- 0.03)x10(-1), (1.97 +/- 0.01)x10(-1), (6.36 +/- 0.06)x10(-2), (8.52 +/- 0.01)x10(-2), and (1.73 +/- 0.01)x10(-1) M, respectively, at 40 degrees C and 25 MPa. It was found that the solubility of Ln(fod)(3)center dot 2H(2)O complexes is higher than that of the corresponding Ln(hfa)(3)center dot 2H(2)O complexes and that the heavy Ln(III) complexes are more soluble than the light Ln(III) ones. These are consistent with the general tendencies that the solubility of metal complexes increases with an increase in the number of fluorine atom in their ligands and that the metal complexes largely shielded by the ligands are more soluble. Furthermore, the solubility of Ln(fod or hfa)(3)center dot 2H(2)O complexes was found to be fairly higher compared with that of other beta-deketonato complexes. This was proposed to be due to the van der Waals interaction between scCO(2) and the fluorine groups in Ln(fod or hfa)(3)center dot 2H(2)O rather than the solvation of CO2. From the present study, the Hfod compound was proposed to be one of promising extractant in the application of SCE method to the decontamination of radioactive wastes. (C) 2015 Elsevier B.V. All rights reserved.