Poly(amidoamine) (PAMAM) dendrimers have attracted attention because of their well-defined molecule structures and chemical versatility, which also complicate the mechanism of interactions between metal ions and PAMAM dendrimers. To further understand the complexation of dendrimers with metal ions, the interactions between Pd2+ ions and G4.5-COOCH3 PAMAM dendrimers were investigated by UV-vis and FTIR spectrophotometric method. The results show that the addition of K2PdCl4 results in covalent attachment of the PdCl3- alcoholysis product of this complex to tertiary amines within the dendrimers under the appropriate conditions. This process was also supported by X-ray photoelectron spectroscopy data of the new complex which indicated a 1 : 3 Pd/Cl ratio. The maximum loading of 80 Pd2+ ions within the G4.5-COOCH3 dendrimers and the best pH value of 8.3 for complexation system are also obtained. Details regarding the Pd species present in solution of different chemical environments are reported. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 112: 2854-2858, 2009