PURPOSE: To reinforce the membrane structure and remarkably inhibit aggregation during storage by adding an aminoalkanesulfonic acid to a liposome dispersion.

CONSTITUTION: A liposome containing encapsulated substances such as an anti- cancer agent, an anti-viral agent, an antibiotics, a peptide hormone and a phospholipid is prepared and the resultant liposome dispersion is preserved by adding an aminoalkanesulfonic acid (e.g. compound such as one represented by formula I) thereto. The above-mentioned method is utilized especially in case of a liposome composed of a phospholipid and/or a glycolipid and cholesterol. The amount of the aminoalkanesulfonic acid added is suitably 0.2-15 pts.wt. based on 100 pts.wt. liposome dispersion. This preservation method is effective to inhibit aggregation in storage of a liposome produced by dispersing a lipid into water in a liquid state.