the hydrophobic parts and the electrostatic interaction between the zwitterionic groups in the case of forming a stable bimolecular membrane vesicle liposome the vesicle permits enclosing a water soluble drug in its inner aqueous phase or permits allowing a recognizing part to be supported on the surface of the liposome membrane so as to make it possible to utilize the vesicle in the drug delivery system particularly if hemoglobin is encapsulated in the internal phase of the vesicle the vesicle can be utilized as an oxygen carrier where the zwitterionic lipid compound of the present invention is utilized as a main component of the membrane of the vesicle it is possible to add sterols as another component of the membrane so as to permit the sterols to act as a stabilizing agent the sterols used in the present invention include for example ergosterol and cholesterol particularly it is desirable to use cholesterol as a stabilizing agent the content of cholesterol is not particularly limited in the present invention however it is desirable for cholesterol to be contained in an amount of 5 to 50 mol more desirably 20 to 50 mol in view of the stability of the vesicle membrane it should also be noted that if a negatively charged lipid is mixed as a component of the membrane the aggregation of the vesicle compounds is suppressed so as to decrease the number.