Following the US Food and Drug Administration's approval of gene therapy drugs, the great potential of disease gene therapy is once again being taken seriously. However, finding a safe and efficient gene delivery vector remains the biggest challenge to successful gene therapy. To overcome this, engineered non-viral gene delivery vectors are continually being developed, despite their lower efficiencies compared with viral vectors. However, the complex biological barriers and instability caused by charge interactions mean that, no major breakthroughs have been made in the clinical development of these non-viral gene vectors. Nevertheless, the functions of the engineered polymer gene carriers are continuously expanding, and success has been achieved with the combined use of therapeutic molecules and targeted delivery. These polymer gene-carrier vectors offer a broader choice of new treatments for diseases ever before.