Hyperbranched dendron (HD) polymers are synthesized using low molecular weight polyethyleneimine (BPEI-L) as a core and used for gene delivery. The obtained polymers display low toxicity and efficient gene delivery at low nitrogen-to-phosphate (N/P) ratios. Using successive attachment of ethyleneimine moieties to a PEI core, the polymer has a lower relative ratio of linear-to-branched structures than in the core PEI. The more extensive branching enables the polymer to condense plasmid DNA into nanostructure complexes with a size of less than or equal to about 100 nm. The complexes are stable and efficient in transfecting cells in the presence of serum. Bioluminescent imaging of in vivo gene expression using a luciferase reporter gene performed in live mice showed gene expression in the liver and in submandibular lymph nodes.