In order to improve DNA transfection/siRNA silencing, a series of novel bifunctional peptides had been designed in the present study. The bifunctional peptides had a complexing moiety (denoted B), and a targeting moiety (denote Y), connected by linker L. All the BLY peptides had the same sequence in region L and Y. Region B was composed of ether a single histidine (H), arginine (R) and lysine (K) residue, denoted Series I, or a combination of them, Series II. These peptides have been shown to be more efficient vectors for DNA/siRNA delivery, especially when assembled with cationic vesicles (DOTMA:DOPE 1:1 molar ratio) into a ternary LPD or LPR complex composing cationic Lipids/bifunctional Peptide/DNA or siRNA. The delivery of these LPDs/LPRs was assessed by luciferase transfection/silencing on lung carcinoma A549 cells. Of a combination of preparation and transfection aqueous solutions, the LPDs/LPRs prepared in water and in NaCl solutions had the same level of transfection/silencing when diluted in Optimem to incubate with cells. However, only the LPDs/LPRs prepared in NaCl solutions showed effective transfection/silencing (proportional to NaCl concentration of up to 0.12 M) when diluted in RPMI-1640 Media containing 10% v/v fetal bovine serum. Of various combinations, the LPDs/LPRs containing Series II peptides appeared to be superior over those containing Series I. Agarose gel electrophoresis showed that the LPDs/LPRs prepared in NaCl solutions afforded more protection against enzyme than those prepared in water without difference in condensation and release. Picogreen fluorescence assay revealed that DNA/siRNA was weakly condensed in LPDs/LPRs when prepared in NaCl solutions due to charge screening effect of salt. Moreover, dynamic light scattering showed that the LPDs/LPRs prepared in NaCl solutions were larger than those prepared in water due to alleviated condensation as shown in picogreen fluorescence assay. Small angle neutron scattering exhibited that the LPDs/LPRs prepared in both water and NaCl solutions had the same single lipid bilayer structure with the same bilayer thickness. The present study suggests that these novel LPDs/LPRs should be further studies in vivo. In particular, 0.12 M NaCl solution is close to isotonic NaCl solution (0.15 M) which can be injected directly into bodies, revealing that those LPDs/LPRs may have potential in clinical therapy of lung cancers.