Liposomes were prepared by adding hydrophilic agents PEG PE, rigidity agent SM in the bilayer membrane for mimetic red cell membrane. In PBS or serum, release of calcein content from liposomes dramatically decreased, which demonstrated increasing membrane stability by adding PEG PE or SM. The ratio b/R of the remains of liposomes in blood to that in RES was used as a parameter of biodistribution in vivo. At 2 h after iv injection, b/R of modified liposomes was enhanced 6.5～13.1 fold. Their clearance half life from blood circulation was delayed 1.6～5.8 fold. The modification of liposome membrane by PEG PE or SM is the favorable condition for drug liposomes to target the non RES.
