The encapsulation characteristics of cerasome, an organic inorganic hybrid vesicle, were clarified using a macromolecular fluorescent marker. The cerasome successfully entrapped the marker molecule in its inner aqueous space over a prolonged period in stark contrast to unstable phospholipid liposomes. In addition, the cerasome maintained its encapsulation ability in the presence of serum containing membrane-destabilizing lipoproteins.