Solvent extraction of platinum(IV) and palladium(II) with tri-n-octylamine(TOA) in o-xylene from 4.0M (Na,H)(Cl, HSO4) has been investigated at 298K in order to compare with similar extraction by trioctylphosphine oxide(TOPO). The dependence of the distribution ratio of platinum(IV) and pal 1adium(II) on TOA, hydrogen ion and chloride ion concentrations suggests the dominant extracted species of these metals would be 2:1 for proto-nated amine : chlorocomplex anion and the extraction should be essentially anion exchange reaction. The extraction constants (Kex = D[H+(T0A)C1 ] 2[C1 ]2), were evaluated as 106-3and 105.8for platinum(IV) and pal ladium(II), respectively. The anion exchange with protonated TOPO salt represented by H(T0P0)2+C1 is less than that with protonated TOA salt by a factor of one order.