Polyallylamine (PAA), a less investigated polycationic polymer along with polyanionic dextran sulfate (DS) has been complexed with DNA into self assembling PAA–DS–DNA complexes with zinc as stabilizing agent. The complexes prepared were characterized by dynamic light scattering and atomic force microscopy and found to have average hydrodynamic diameter of 150 nm with polydispersity below 0.2, i.e. nanoplexes with narrow size distribution. As expected, the zeta potential values increased with the increase in the PAA in the nanoplexes. Further, PAA–DS–DNA nanoplexes were investigated for in vitro transfecting efficacy on HEK 293 cells. The nanoplexes were found to have better gene transfer efficacy compared to the DNA–PAA complex and commercially available transfecting agent lipofectin. The cytotoxicity was also decreased considerably as revealed by MTT colorimetric assay. The nanoplexes prepared with PAA to DS ratio of 2 were found to be most efficient transfecting agent.