Hafnium can be selectively extracted over zirconium from strong sulfuric acid solutions by D2EHPA or PC 88A. Solvent extraction experiments have been performed to identify the reaction of Hf from strong sulfuric acid solutions (1 to 7 M) by these two extractants. Hafnium extraction was gradually decreased and then increased again with the increase of sulfuric acid concentration. By applying a slope method, the extracted Hf species was proposed to be HfA(4)center dot(HA)(2) by D2EHPA and Hf(HSO4)(2)A(2)center dot(HA)(2) by PC 88A, respectively. This difference in the nature of the extracted species was verified by FT-IR spectra.