Polymeric amines and complex amine containing system are actively studied and applied as gene delivery agents in gene therapy and genetic engineering. Optimizing polymer - nucleic acid ratio is the key stage in elaboration of procedures in this area. Application of fluorescent tagged oligonucleotides is widespread approach which allows to visualize nucleic acid in gel electrophoresis experiments and to find conditions of the full binding of the nucleic acid. We suggest to use succinimidyl ester of 7-(diethylamino)coumarin-3-carboxylic acid as an agent for fluorescent labeling of polymeric amines and to use the tagged polymers in optimizing polymer - nucleic acid ratio. This approach allows to see unbound polymer and to study various nucleic acids in interaction with the same polymer. •Labeling of gene delivery agents with fluorescence groups increases efficiency of optimization of gene delivery compositions.•Polymeric amines tagged with succinimidyl ester of 7-(diethylamino)coumarin-3-carboxylic acid are suitable for study polymer - nucleic acid interaction with gel electrophoresis.