The transfection of DNA in gene therapy largely depends on the possibility of obtaining its condensation. The details of nanoparticle formation are essential for functioning, as mediated by the diverse elements containing molecular structure, ionic strength in mediums, and condensing motivator. Here, we report two kinds of DNA condensing agents based on simple cyclic/rigid polyamine molecules, having evaluated their structural effect on nanoparticle formation. The reversible condensation-dissociation process was achieved by ion switching, attributing to a possible condensing mechanism-competitive building of external hydrogen bonds. Using poly[(dA-dT)(2)] and poly[(dG-dC)(2)] as substrates, respectively, circular dichroism (CD) signals clearly presented dissimilar interactions between polyamines and both rich sequences, implying potential preference for G-C sequence. The presence of divalent ion Zn2+ as an efficient motivator accelerated the achievement of DNA condensation, and an accessible schematic model was depicted to explain the promotion in detail. In addition, by comparison with the behaviors of linear polyamines, differences between condensation and aggregation were explicitly elucidated in aspects of morphology and surface charges, as well as induced condition. The present work may have the potential to reveal the precise mechanism of DNA nanoparticle formation and, in particular, be applied to gene delivery as an efficient nonviral vector.