The present study deals with the synthesis and characterization of six tri-palladium complexes code named MH3, MH4, MH5, MH6, MH7 and MH8 that contained two planaramine ligands bound to the central or each of the terminal metal ions. The activity of the compounds against human cancer cell lines: A2780, A2780cisR and A2780ZD0473R, cell uptake, levels of DNA-binding and nature of interaction with salmon sperm and pBR322 plasmid DNA have also been determined. Whereas cisplatin binds with DNA forming mainly intrastrand GG adduct that causes local bending of a DNA strand, the tri-palladium complexes are expected to bind with DNA forming a number of long-range interstrand GG adducts that would cause a global change in DNA conformation. Among the designed complexes, MH6 that has two 2-hydroxypyridine ligands bound to each of the two terminal palladium ions is found to be most active. The compound also has the highest cell uptake and Pd-DNA binding levels. In contrast, MH8 which has two 4-hydroxypyridine ligands bound to each of the two terminal palladium ions is found to be least active. The results indicate that, as applied to the terminal metal centres, 2-hydroxypyridine would be more activating than 4-hydroxypyridine perhaps because of greater protection provided to the terminal centres from coming in contact with the solvent molecules. In contrast, when bound to the central metal centre, 4-hydroxypyridine appears to play a slightly greater activating role than 2-hydroxypyridine or 3-hydroxypyridine, suggesting that non-covalent interactions such as hydrogen bonding associated with the ligand rather than its steric effect may be a more important determinant of antitumour property. The results illustrate structure-activity relationships and suggest that the tri-palladium complex containing two 2-hydroxypyridine ligands bound to each of the three metal centres or the compound that contains two 2-hydroxypyridine ligands bound to each of the two terminal metal centres and two 4-hydroxypyridine ligands bound to the central metal centre, may be much more active than any of the designed complexes.