The present study strongly relates to ongoing research on the development of cationic polymers which are of great interest due to their enormous potential for biomedical applications, especially as non-viral vectors for gene therapy, antimicrobial agents and active components in DNA sensing devices. The current paper demonstrates that a functional group approach can be successfully realized in a free-radical copolymerization process to prepare cationic copolymers with a desired composition of amine groups, which can be protonated in water thus, providing electrostatic interactions between a polycation and DNA. Three replicas of the cationic copolymer, acrylamide/3-(N,N-dimethylaminopropyl)-acrylamide (AADMAPA), were synthesized using this strategy. The values of average molecular mass and polydispersity index, are similar for the replicas, averaged to 24 000 ± 2000 g mol⁻¹ and 1.5 ± 0.1, respectively. The copolymer composition according to ¹H-NMR (D₂O), was corresponded to the molar ratio of initial monomers. The dynamic light scattering studies and zeta potential measurements confirmed that in water positively charged AADMAPA/DNA polyplexes are formed at N/P > 2.2: the formed particles have bimodal distributions with the average diameters of 70 and 700 nm. Zeta potential measurements indicated that the point of zero charge (isoelectric point) is close to N/P ≅ 2.2. According to the atomic force microscopy positively charged AADMAPA/DNA polyplexes have axially symmetric shapes.