Successful gene therapy depends on efficient gene transfer vectors. Viral vectors and non-viral vectors have been investigated extensively. Cationic lipids are non-viral vectors, which resemble traditional pharmaceuticals, display little immunogenicity, and have no potential for viral infection. However, toxicity and low transfection efficiency are two barriers limiting the clinical applications of cationic lipids. Over the last decade, hundreds of cationic lipids have been synthesized to address these problems. In this brief review, we summarized recent research results concerning the structures of DNA / liposomes complexes, some important strategies used to design different classes of cationic lipids, and use of disulfide cationic lipids in plasmid DNA delivery.