Liposomes composed of phosphatidylcholine (PC) and phosphatidylglycerol (PG) were prepared to examine the effects of lipid composition on surface properties of the liposomes and entrapment efficiency of proteins into the liposomes. Lipid composition was found to influence the amount and mode of proteins entrapped into the PC/PG liposomes, as well as the surface properties of the liposomes. Both electrostatic and non-electrostatic interactions between protein and liposome played important roles in the entrapment of protein into the PG-containing liposomes, and the amount of proteins adsorbed electrostatically on the PG-containing liposomes was also influenced by lipid composition.