A study on the basicity and complexing ability of some poly(amidoamines) and their low-molecular weight analogues has been performed in aqueous solution. “Real” basicity constants have been determined for the polymers. This unusual behaviour has been attributed to their particular structure. The basicity constants of the polymers are always slightly lower than those of the corresponding models. The complexing ability of both macromolecules and models towards Cu(II) and Ni(II) ions in aqueous solution depends upon both the number of vicinal tertiary amino groups and the flexibility of the structure.