In chloride media, chloropalladium(II) species are adsorbed onto tannin gel particles through an inner-sphere redox reaction mechanism containing the intermediate step, formation of a ligand-substituted Pd(II)-tannin complex. In this Pd(II) adsorption process, it was observed that the adsorption rate can be increased by introducing Br-, a softer ligand than Cl-, into the aqueous chloride solution. The formation of mixed-ligand palladium(II) complexes accelerates the rate of ligand-substitution reactions with the hydroxyl groups of tannin gel by the trans effect. The adsorption condition can be optimized by controlling the [Brtot]/[Cltot] ratio, in which the predominant Pd(II) species are bromo-chloro palladium(II) complexes, the favorable species for the trans effect.