We have examined the extraction selectivity towards various metals of N-dodecylaniline, which has an aromatic secondary amine moiety, a weaker base than an aliphatic secondary amine. The selectivity of N-dodecylaniline in toluene for extraction from hydrochloric acid solution was examined by a batchwise method at 300 K, and Pt(IV), Pd(II) and Au(III) were found to be quantitatively extracted, while base metals were not extracted. Therefore, N-dodecylaniline as an extractant was found to be a highly selective for Pt(IV), Pd(II) and Au(III) over base metals. In the extraction of Pt(IV), it was suggested that different platinum complexes were extracted at low and high concentrations of hydrochloric acid. Pt(IV) was found to be extracted by the following extraction reactions from hydrochloric acid solution. (RN) over bar + H+ + Cl- reversible arrow (RNHCl) over bar K-1 K-1 = 1.10(mol dm(-3))(-2) 2 (RN) over bar + PtCl5- reversible arrow <((RN)(2)PtCl4)over bar> + Cl- K-2 K -2.90 x 10(2)(mol dm(-3))(-1) 2 (RNHCl) over bar + PtCl62- reversible arrow <((RNH)(2)PtCl6)over bar> + 2Cl(-) K-3 K-3 -1.23 x 10(4)(-) Back extraction of the extracted Pt(IV) from the loaded organic phase was examined using various stripping agents, of which aqueous thiourea and thiourea containing HCl were found to be effective.