Abstract: Efficiency of non-viral gene delivery based on chitosan and chitosan derivatives as DNA condensing carrier is dependent on a series of factors, such as complex size, the charge ratio of chitosan/DNA, molecular mass of chitosan, the degree of chitosan deacetylation, pH and serum concentration of the transfection medium. Through modifying the chitosan in a certain extent, we can change the efficiency of transfection. Studies on transfection condition, efficiency and mechanism using chitosan and chitosan derivatives as transfection agents are reviewed.