Substitution reactions of the complexes [Pd(bpma)(H2O)]2+, [Pd(bpma)Cl]+, [Pd(dien)(H2O)]2+ and [Pd(dien)Cl]+, where bpma = bis(2-pyridylmethyl)amine and dien = diethylentriamine or 1,5-diamino-3-azapentane, with some nitrogen-donor ligands such as triazole, pyrazole, pyrimidine, pyrazine and pyridazine, were studied in an aqueous 0.10 M NaClO4 at pH 2.8 using variable-temperature and -pressure stopped-flow spectrophotometry. The second-order rate constants indicate that the Pd(II) complexes of bpma, viz. [Pd(bpma)(H2O)]2+ and [Pd(bpma)Cl]+, are more reactive than the complexes of dien, viz. [Pd(dien)(H2O)]2+ and [Pd(dien)Cl]+. Also, the aqua complexes, [Pd(bpma)(H2O)]2+ and [Pd(dien)(H2O)]2+, are much more reactive than the corresponding chloro complexes. The most reactive nucleophile of the five-membered rings is triazole and for the six-membered rings the most reactive one is pyridazine. Activation parameters were determined for all reactions and the negative entropies and volumes of activation (ΔS‡, ΔV‡) support an associative ligand substitution mechanism. The crystal structure of [Pd(bpma)(H2O)](ClO4)2·2H2O was determined by X-ray diffraction. Crystals are monoclinic with the space group P21/c. The coordination geometry of [Pd(bpma)(H2O)]2+ is distorted square-planar. The Pd–N (central) bond distance, 1.958(5) Å, is shorter than the other two Pd–N distances, 2.007(5) and 2.009(5) Å. The Pd–O distance is 2.043(5) Å.