Gene therapy based on small interfering RNA (siRNA) has emerged as an exciting new therapeutic approach. However, insufficient cellular uptake and poor stability have limited its usefulness. Here, we report efficient delivery of siRNA via the use of cationic liposomes that contain a new PEG-lipid. The new lipid, poly-l-arginine-conjugated polyethylene glycol (PLR-PEG), was synthesized. To confirm the synthesis of the amino acid-conjugated PEG-lipid, (1)H NMR and gel permeation chromatography (GPC) were performed. Cationic liposomes as non-viral vectors were formulated using the cationic lipids 1,2-dioleoyl-3-trimethylammonium propane (DOTAP), 1,2-dioleoyl-sn-glycero-3-phosphoethanolaminepropane (DOPE), cholesterol (Chol) and PLR-PEG. Physicochemical properties of cationic liposomes were investigated. A GFP siRNA was used as a model siRNA to test the efficiency of cationic liposome-mediated siRNA delivery. The liposomes could enhance delivery efficiency and decrease cytotoxicity at an optimized lipid composition. The new cationic liposome formulation using a new PEG-lipid (PLR-PEG) showed not only enhanced intracellular delivery of siRNA but also decreased cytotoxicity in H4II-E and HepG2 cell lines. The GFP siRNA delivered by new cationic liposomes using PLR-PEG was effective in reducing the GFP protein expression levels of the gene. These results suggest that the new cationic liposomes could be used for efficient delivery of siRNA therapeutics.