The present invention relates to a method for producing a composition containing a complex between a membrane composed of a lipid monolayer (reversed micelle) and a nucleic acid, and a lipid membrane for encapsulating the complex therein, comprising the following steps A to D: Step A: preparing a complex between the nucleic acid and a liposome comprising a cationic lipid represented by the formula (I) and/or a cationic lipid other than cationic lipid represented by the formula (I) Step B: preparing a dispersion liquid by dispersing the complex in water or ethanol aqueous solution Step C: preparing a solution by dissolving the formula (I) and/or the cationic lipid other than cationic lipid represented by the formula (I) in ethanol or an ethanol aqueous solution and Step D: mixing the dispersion liquid and the solution, and optionally adding water wherein the formula (I) is (wherein: R 1 and R 2 are, the same or different, each linear or branched alkyl, alkenyl or alkynyl having 12 to 24 carbon atoms, X 1 and X 2 are hydrogen atoms, or are combined together to form a single bond or alkylene, X 3 is absent or is alkyl having 1 to 6 carbon atoms, or alkenyl having 3 to 6 carbon atoms, when X 3 is absent, Y is absent, a and b are 0, L 3 is a single bond, R 3 is alkyl having 1 to 6 carbon atoms, alkenyl having 3 to 6 carbon atoms, or alkyl having 1 to 6 carbon atoms or alkenyl having 3 to 6 carbon atoms substituted with 1 to 3 substituent(s), which is(are), the same or different, amino, monoalkylamino, dialkylamino, trialkylammonio, hydroxy, alkoxy, carbamoyl, monoalkylcarbamoyl, or dialkylcarbamoyl, and L 1 and L 2 are -O-, Y is absent, a and b are, the same or different, 0 to 3, and are not 0 at the same time, L 3 is a single bond, R 3 is alkyl having 1 to 6 carbon atoms, alkenyl having 3 to 6 carbon atoms, or alkyl having 1 to 6 carbon atoms or alkenyl having 3 to 6 carbon atoms substituted with 1 to 3 substituent(s), which is(are), the same or different,
