Abstract: The present invention provides a liposome stabilizing agent comprising a lipid of carboxylic acid type represented by the following general formula: (wherein any one of R1, R2 and R3 represents the following general formula: [wherein M represents a hydrogen atom or a monovalent cation and m, which defines the methylene chain length, represents an integer of 1 to 5], and the other two each represent an chain hydrocarbon group, A1, A2 and A3 are each independently selected from the group consisting of C(O)O, CONH and NHCO, and n, which defines the methylene chain length, represents an integer of 1 to 3), as well as liposomes containing the liposome stabilizing agent and a kit comprising the liposome stabilizing agent.