A liposome preparation is provided. This liposome preparation is capable of stably encapsulating a drug which is unstable under an acidic condition, and such stable encapsulation is realized without detracting the effect realized by the modification of the membrane by a hydrophilic macromolecule such as stability in blood. More specifically, the liposome preparation comprises a unilamellar vesicle formed from a lipid bilayer comprising a phospholipid as its main membrane component, and an interior aqueous phase of the vesicle at a pH of up to 5. The liposome has a drug loaded therein, and the vesicle is modified with a hydrophilic macromolecule only on its exterior surface.
