Recent rapid development of molecular biology together with the steady progress of genome projects has been given us some essential and revolutionary informations of gene to elucidate all the biological phenomena at the molecular level. Under these circumstances, gene transfection has become one of the fundamental technologies indispensable to the basic research of medicine and biology. Human gene therapy has been performed with plasmid DNA alone or the virus vector constructs. However, there are clinical limitations, low gene expression of plasmid DNA and the immunogenicity and toxicity of virus itself or the possible mutagenesis of cells transfected. Therefore, several non-viral vectors of synthetic materials have been explored to enhance the transfection efficiency of gene into mammalian cells both in vitro and in vivo. In this paper, as one research trial, the controlled release of plasmid DNA is overviewed. A new system of plasmid DNA release with a biodegradable hydrogel is explained while the biological activity of a plasmid DNA of hepatocyte growth factor antagonist, NK4, is augmented by use of the release system.