Polycations can condense with DNA by self-assembly

form polyplexes nanoparticles spontaneously as a result of electrostatic interactions and protect DNA from degradation by DNase.They have great advantages used for gene delivery such as ease of synthesis

cel/l tissue targeting

low immune response

Stableness in storage

and unrestricted plasmid size.Polycations as non-viral gene vectors can be divided into two types:synthetic polycations such as PEI

PLL

and PAMAM;and natural polycations such as chitosan

its derivative and gelatin.So development on polyplexes nanoparticles used as controlled gene delivery systems are discussed with emphasis on mechanism of polycation-mediated cell entry and targeting strategies of polycations

also several polyplexes are evaluated with respect to their characters and transfection efficiency

at last it can conclude that nontoxic natural gene vectors should be the focus of studies in the future.